Nevermind. I found my answer. It'd been awhile since I was actually configuring mamewah, so apologies...
Basically, it's in the mamewah.cfg file. Under this section heading:
# any form
VOLUME_DOWN
VOLUME_UP
VOLUME_MUTE
PLAY_OR_PAUSE
PREVIOUS_TRACK
NEXT_TRACK
REWIND_TRACK
FF_TRACK
So assign a key such as:
NEXT_TRACK DIK_1
And there you go.
AJ