url_outbound_alter_example.php

<?php

/**
* Implements hook_url_outbound_alter() - from URL Alter module
*/
function YOURMODULE_url_outbound_alter(&$path, &$options, $original_path) {

  // Rewrite paths for rices4peru.com
  if ($_SERVER['HTTP_HOST'] == "www.rices4peru.com") {
    $options['absolute'] = TRUE;
    $options['base_url'] = 'http://www.drupal.rices2peru.com';
  }

}

?>

Drupal 7 only ;).

Drupal 6 have function custom_url_outbound_alter() but it very slow and teriable.