Thematic: Show archives in menu?

I’m trying to modify the menu in the Thematic-theme to add a menu item with Archives. I found a working piece of code to do the same thing but with Categories, but when I try to modify this code to show Archives it doesn’t work as good.

I want it to look like this:

| Archive
---------------------|
| September 2010 (2) |
| August 2010 (1)    |

But now it’s like this with two separate buttons:

| September 2010 (2) | August 2010 (1)
--------------------|-----------------|

My code looks like this:

function add_childtheme_archive_menu($args) {
    $archives = wp_get_archives('echo=0&show_post_count=1&title_li=<li><a href="#">Arkiv</a>');
    $args .= $archives . '</li>';
    return $args;
    } 

add_filter('wp_list_pages','add_childtheme_archive_menu');

The working code I found for categories is:

function add_childtheme_category_menu($args) {
    $categories = wp_list_categories('echo=0&title_li=<li><a href="#">Kategorier</a>');
    $args .= $categories . '</li>';
    return $args;
    } 

add_filter('wp_list_pages','add_childtheme_category_menu');

What should I change to make it work right? And otherwise, is there a nice plug-in available for Archives which will give a similar result?