Can you really append # to

wp_list_categories( 'include=13&title_li=&style=none&echo=0')?

In final link groups link may need to look like: domain/categories/somepost#

Adding a filter for that creation of wordpress_list_groups could do that within the php. You should use preg_replace along with a regex for locating the web addresses. For instance:

add_filter('wp_list_categories', 'filter_categories', 10, 2);

to include your "filter_groups" function towards the filter - don't refer to it as filter groups, refer to it as something unique like sjn_filter_groups.

function filter_categories($output, $args=array()){
      return preg_replace('/(\<a\shref=\"?[^\>]+?)\"/', '$1#"', $output);

Will require the output, search it for href web addresses, take away the '"' and add '#' and '"' back on. I really hope this can help!