Hmm...unlikely. FCEU basically runs games at one guaranteed resolution, with one guaranteed orientation, so I know I have Z amount of screen space at position (X,Y) to place the buttons, and that they'll be usable if I place them there. IMO it would be very difficult to find space to place them in a consistent and helpful manner with xmame.
However, there is hope for a snes emulator if I can do something similar with zsnes or snes9x.