How to create a Sky sub-theme?

OK after some try and some studies on Zen theme... I've got a solution.

With this modification you'll be able to create subdirectories into sky theme dir, then copying style.css, images/ and css/ directories.
Doing this will be enough to have a new theme based on sky with its preferences (for menus, breadcrumb fonts and other settings).

template.php must be edited like this:

/*
 * Initialize theme settings
 */
if (is_null(theme_get_setting('sky_layout'))) {
  global $theme_key;

  // Save default theme settings
  $defaults = array(
    'sky_breadcrumbs' => 0,
    'sky_breadcrumbs_sep' => '»',
    'sky_font' => 'lucida',
    'sky_font_headings' => 'lucida',
    'sky_font_size' => '12px',
    'sky_header_height' => 'auto',
    'sky_layout' => 'fixed_960',
    'sky_title' => 1,
    'sky_nav_alignment' => 'center',
    'sky_sub_navigation_size' => '15em',
    'sky_wireframe' => 0,
  );
	$defaults = variable_get('theme_sky_settings' , $defaults);
  variable_set(
    str_replace('/', '_', 'theme_'. $theme_key .'_settings'),
    array_merge($defaults, theme_get_settings($theme_key))
  );
  // Force refresh of Drupal internals
  theme_get_setting('', TRUE);
}

// Appearance Stylesheet.  Controls the colors, fonts and borders of the theme
if (theme_get_setting('sky_wireframe') == 0) {
	global $theme_key;
	if ($theme_key == 'sky') {
		drupal_add_css(path_to_theme() .'/css/appearance.css', 'theme', 'all', TRUE);	
	}
	else {
		drupal_add_css(path_to_theme() . '/' . $theme_key . '/css/appearance.css', 'theme', 'all', TRUE);	
	}
}

I've also attached a patch but I dunno if done correctly... :p