Enhancement request: multi-select custom post types

Enhancement request for the Recent Posts Widget:

Allow user to multiselect from all custom post types. In my case, I want a widget for all post types in one list. I can't do this currently (I don't think...). But just a selection for "all" won't do it either, because there are cases where I want some post types but not others.

Guidance on a hack would be appreciated for now, but I think this would be a valuable enhancement.

Great work!