Combining depth and specifc pages in wp_list_pages

I am using wp_list_pages('include=2,4,6') to build a specific navigation bar. What I want to do now is also show depth=2 so that I can manage a drop down list from this pages where there are children. But of course because I’m specifing particular pages at the top level the function is ignoring the depth.

Can anyone think of a way around this without having to code in every relevant child ID?