Ok, thanks moshu 🙂
Its not that many subcategories so I guess it could work anyway. But it would been nice with an easier solution. Maybe a task for a new plugin – perhaps I will try to create one some day 🙂
Dont know if this helps, but you can use the_category_rss() int the Loop:
http://codex.wordpress.org/Template_Tags/the_category_rss
or in the wp_lists_cats() there is an argument for feeds and feed-image:
http://codex.wordpress.org/Template_Tags/wp_list_cats
