I have almost exactly what you want: Deskfolders.

Aparently buggy on some systems, but I've had no issues.
Just set the root to the folder you want, then disable browsing.

An alternate option is to call a dynamicfolder popup in either your main popup code (theme independent), or make it theme independent and popup in a corner/with a special hotkey, etc.

You wouldn't have a bar, but you wouldn't have to muck about in rc files to add things.