Ugly as sin module to override drupal directory creation on install...broken for migrate though

mymodule.drush.inc

<?php
/**
 * Implementation of hook_provision_drupal_create_directories().
 *
 * Make the directory create phase of a site install web cluster ready.
 * A patch to provision is needed.
 * @url http://drupal.org/files/issues/provision_drupal_create_directories.patch
 */
function mymodule_provision_drupal_create_directories(&$dirs, $url) {
  $web_group = d('@server_master')->web_group;

  $path = "sites/$url";
  if (!is_dir($path)) {
    provision_file()->mkdir($path)
      ->succeed('Created <code>@path</code>')
      ->fail('Could not create <code>@path</code>', 'DRUSH_PERM_ERROR');
  }

  provision_file()->chmod($path, $dirs[$path], false)
    ->succeed('Changed permissions of <code>@path</code> to @perm')
    ->fail('Could not change permissions <code>@path</code> to @perm');
  unset($dirs[$path]);

  $link = 'cache';
  $path = d()->root . '/' . $link;
  if (!is_link($path) && !preg_match("/hostmaster/", $path)) {
    drush_set_error("cache directory $realpath is not a link");

    provision_file()->symlink($dir, d()->root . '/' . $link)
      ->succeed('linked <code>@path</code> to <code>@target</code>')
      ->fail('Could not create link to <code>@path</code> from <code>@target</code>', 'DRUSH_PERM_ERROR');
  }

  $symlink = array(
    "sites/$url/files",
    "sites/$url/private",
  );
  foreach ($symlink as $link) {
    if (isset($dirs[$link])) {
      unset($dirs[$link]);
    }

    $dir = '/var/lib/sitedata/aegir/' . "$url/" . basename($link);

    if (!is_dir($dir)) {
      provision_file()->mkdir($dir)
        ->succeed('Created <code>@path</code>')
        ->fail('Could not create <code>@path</code>', 'DRUSH_PERM_ERROR');

        $path = '/var/lib/sitedata/aegir/' . $url;
        $perm = 0755;
        provision_file()->chmod($path, $perm, FALSE)
          ->succeed('Changed permissions of <code>@path</code> to @perm')
          ->fail('Could not change permissions <code>@path</code> to @perm');
    }

    if (is_link($link)) {
      $realpath = realpath($link);
      if ($realpath == $dir) {
        $group_id = filegroup($dir);
        $group_info = posix_getgrgid($group_id);
        if (!empty($group_info['name']) && $group_info['name'] != $web_group) {
          provision_file()->chgrp($dir, $web_group, FALSE)
            ->succeed('Changed group ownership of <code>@path</code> to @gid')
            ->fail('Could not change group ownership <code>@path</code> to @gid');
        }
        continue;
      }
      else {
        drush_log(t('Link <code>@link</code> does\'t point to sitedata directory <code>@dir</code>, hopefully fixing now...', array('@link' => $link, '@dir' => $dir)), 'error');
        provision_file()->symlink($dir, d()->root . '/' . $link)
          ->succeed('linked <code>@path</code> to <code>@target</code>')
          ->fail('Could not create link to <code>@path</code> from <code>@target</code>', 'DRUSH_PERM_ERROR');
        continue;
      }
    }

    // If the directory already exists, then we need to move all the existing
    // contents into the sitedata directory before we remove it.
    $realpath = realpath($link);
    if ($realpath && !is_link($realpath)) {
      if (!drush_shell_exec('cd %s && tar -c * | tar -x -C %s', $realpath, $dir)) {
        drush_set_error("Cannot move contents out from $realpath");
        drush_set_error(print_r(drush_shell_exec_output(), true));
        continue;
      }
      // Delete the old <platform>/sites/<site>/<directory>
      if (!drush_shell_exec('rm -rf %s', $realpath)) {
        drush_set_error("Cannot rm $realpath");
        drush_set_error(print_r(drush_shell_exec_output(), true));
        continue;
      }
    }

    // Finally, make the symlink.
    provision_file()->symlink($dir, d()->root . '/' . $link)
      ->succeed('linked <code>@path</code> to <code>@target</code>')
      ->fail('Could not create link to <code>@path</code> from <code>@target</code>', 'DRUSH_PERM_ERROR');

    //provision_file()->chgrp($dir, $web_group, FALSE)
    provision_file()->chgrp($dir, $web_group, TRUE)
      ->succeed('Changed group ownership of <code>@path</code> to @gid')
      ->fail('Could not change group ownership <code>@path</code> to @gid');

    // Ensure correct permissions
    $perm = 02770;
    //provision_file()->chmod($dir, $perm, TRUE)
    provision_file()->chmod($dir, $perm, FALSE)
      ->succeed('Changed permissions of <code>@path</code> to @perm')
      ->fail('Could not change permissions <code>@path</code> to @perm');
  }
}

provision_drupal.drush.inc.patch

diff --git a/platform/provision_drupal.drush.inc b/platform/provision_drupal.drush.inc
index 071806e..e4baaff 100644
--- a/platform/provision_drupal.drush.inc
+++ b/platform/provision_drupal.drush.inc
@@ -237,6 +237,9 @@ function _provision_drupal_create_directories($url = NULL, $profile = NULL) {
     "sites/$url/private/temp"
   );
 
+  // Allow other commands to add or alter the directories to be created.
+  drush_command_invoke_all('provision_drupal_create_directories', $mkdir, $url);
+
   foreach ($mkdir as $path => $perm) {
     if (!is_dir($path)) {
       provision_file()->mkdir($path)