Load only the submenus under given menu
$main_menu_tree = menu_tree('main-menu');
foreach ($main_menu_tree as $key =&gt; &amp;$main_menu_item) {
    if (is_numeric($key)) {
        $main_menu_item['#below']['#theme_wrappers'][0] = 'some_other_theme_wrapper';
    }
}
print drupal_render($main_menu_tree);


If you have array of main menu active trails you can use foreach to loop through the array print menus and their sub menus.