I've added .xml for that in the text box listed under
Add here strings (not a filename) that forces a page not to be cached. For example, if your URLs include year and you dont want to cache last year posts, it’s enough to specify the year, i.e. ’/2004/’. WP-Cache will search if that string is part of the URI and if so, it will not cache that page.
on the Advanced page, and that works for me.