A Sample short profile that auto-fills the DB form, its a little ugly.

shortprofile.info

; dpg ::: http://drupal.org/user/1059226
; Example Short Profile -- hides database configuration page.
;
; This bears mentioning more than once. See http://drupal.org/node/1153646


name = Short Profile
description = A short profile, it removes DB settings page.
core = 7.x
dependencies[] = block
dependencies[] = color
dependencies[] = comment
dependencies[] = contextual
dependencies[] = dashboard
dependencies[] = help
dependencies[] = image
dependencies[] = list
dependencies[] = menu
dependencies[] = number
dependencies[] = options
dependencies[] = path
dependencies[] = taxonomy
dependencies[] = dblog
dependencies[] = search
dependencies[] = shortcut
dependencies[] = toolbar
dependencies[] = overlay
dependencies[] = field_ui
dependencies[] = file
dependencies[] = rdf
files[] = shortprofile.profile

shortprofile.profile

<?php


function shortprofile_install() {
  include_once DRUPAL_ROOT . 'profiles/minimal/minimal.install';
  minimal_install();
}

function shortprofile_install_tasks_alter(&$tasks, $install_state) {
  // Hide the database configuration step.
  $tasks['install_settings_form']['display'] = FALSE;


  // See this issue, that we cant just form_alter the database configuration
  // page: http://drupal.org/node/1153646
  //
  // We supply our own database configuration form -- and by doing so also need
  // to supply _submit and _validate functions herein. We just copy the
  // source code from those functions into ours.
  //
  // If you use the *hack* in the above issue queue you dont need to do this
  // function override of this settings form. You can just do a simple:
  // system_form_install_settings_form() in your installation profile and
  // supply default values I believe.
  //
  // But dragons be there! 'Ye be warned. It's not Kosher.
  $tasks['install_settings_form']['function'] = 'shortprofile_install_settings_form';
}



/**
 * Our custom database form. We force our own local values. Why, who knows.
 */
function shortprofile_install_settings_form($form, &$form_state, &$install_state) {
  global $databases;

  $profile = $install_state['parameters']['profile'];
  $install_locale = $install_state['parameters']['locale'];

  drupal_static_reset('conf_path');
  $conf_path = './' . conf_path(FALSE);
  $settings_file = $conf_path . '/settings.php';


// I added this line with our defaults.
$databases['default']['default'] = array(
  'driver'   => 'mysql',
  'database' => 'drupal7_profiletest',
  'username' => 'dev_user',
  'password' => 'dev',
  'host'     => 'localhost',
  'port'     => '',
  'prefix'   => '',
);
// The rest of this function is almost the same ....


  $database = isset($databases['default']['default']) ? $databases['default']['default'] : array();

  drupal_set_title(st('Database configuration'));

  $drivers = drupal_get_database_types();
  $drivers_keys = array_keys($drivers);

  $form['driver'] = array(
    '#type' => 'radios',
    '#title' => st('Database type'),
    '#required' => TRUE,
    '#default_value' => !empty($database['driver']) ? $database['driver'] : current($drivers_keys),
    '#description' => st('The type of database your @drupal data will be stored in.', array('@drupal' => drupal_install_profile_distribution_name())),
  );
  if (count($drivers) == 1) {
    $form['driver']['#disabled'] = TRUE;
    $form['driver']['#description'] .= ' ' . st('Your PHP configuration only supports a single database type, so it has been automatically selected.');
  }

  // Add driver specific configuration options.
  foreach ($drivers as $key => $driver) {
    $form['driver']['#options'][$key] = $driver->name();

    $form['settings'][$key] = $driver->getFormOptions($database);
    $form['settings'][$key]['#prefix'] = '<h2 class="js-hide">' . st('@driver_name settings', array('@driver_name' => $driver->name())) . '</h2>';
    $form['settings'][$key]['#type'] = 'container';
    $form['settings'][$key]['#tree'] = TRUE;
    $form['settings'][$key]['advanced_options']['#parents'] = array($key);
    $form['settings'][$key]['#states'] = array(
      'visible' => array(
        ':input[name=driver]' => array('value' => $key),
      ),
    );
  }

  $form['actions'] = array('#type' => 'actions');
  $form['actions']['save'] = array(
    '#type' => 'submit',
    '#value' => st('Save and continue'),
    '#limit_validation_errors' => array(
      array('driver'),
      array(isset($form_state['input']['driver']) ? $form_state['input']['driver'] : current($drivers_keys)),
    ),
// I Edited this line, to point ot our custom submit function.
    '#submit' => array('shortprofile_install_settings_form_submit'),
  );

  $form['errors'] = array();
  $form['settings_file'] = array(
    '#type' => 'value',
    '#value' => $settings_file,
  );

  return $form;
}


/**
 * A custom validate function, copied from Core.
 */
function shortprofile_install_settings_form_validate($form, &$form_state) {
  $driver = $form_state['values']['driver'];
  $database = $form_state['values'][$driver];

// I added this line, setting a default password in the _form() function
// didn't appear to work on the screen.
$database['password'] = 'dev';

  $database['driver'] = $driver;

  // TODO: remove when PIFR will be updated to use 'db_prefix' instead of
  // 'prefix' in the database settings form.
  $database['prefix'] = $database['db_prefix'];
  unset($database['db_prefix']);

  $form_state['storage']['database'] = $database;
  $errors = install_database_errors($database, $form_state['values']['settings_file']);
  foreach ($errors as $name => $message) {
    form_set_error($name, $message);
  }
}



/**
 * Custom submit function. Copied from Core install_settings_form_submit().
 */
function shortprofile_install_settings_form_submit($form, &$form_state) {
  global $install_state;

  // Update global settings array and save.
  $settings['databases'] = array(
    'value' => array('default' => array('default' => $form_state['storage']['database'])),
    'required' => TRUE,
  );
  $settings['drupal_hash_salt'] = array(
    'value' => drupal_hash_base64(drupal_random_bytes(55)),
    'required' => TRUE,
  );
  drupal_rewrite_settings($settings);
  // Indicate that the settings file has been verified, and check the database
  // for the last completed task, now that we have a valid connection. This
  // last step is important since we want to trigger an error if the new
  // database already has Drupal installed.
  $install_state['settings_verified'] = TRUE;
  $install_state['completed_task'] = install_verify_completed_task();
}