Comment 44 for bug 597825

http://groups.google.com/group/microsoft.public.win32.programmer.ui/browse_thread/thread/ccc6cfeb44423ee2/c51ac91dc66e03f8?lnk=gst&q=WM_UPDATEUISTATE#c51ac91dc66e03f8

seems like you get to fire the event yourself. If that's not the right answer, there's a guy from discussions.microsoft.com who's been answering questions about it.