I would also like to implement something similiar. Whist I agree I can use an additional library, it seems a waste given that the exisiting menu forfills my needs perfectly. All the pop up menus i've experimented with don't look as good and just add bloat/complexity to a project. Given that the "activity.openmenu" function opens at the top right of the screen when using the standard actionbar, it surely can't be hard to allow the same location when using a custom bar?
Ideally it would be great if we could specify an X,Y loaction to open at, but failing that even a "TopRight", or "BottomCentered" type option would be great. It surely would also be a really simple implementation?