Well, I have no qualifications in micro console building, but maybe something like kinda like a Wiimote nunchuck seems like it would make the most sense? I'm thinking something about a little bigger than a disposable lighter with a screen up top, a D pad on the front and two buttons on the back... or maybe the side? Add some lower thumb buttons for less used functions.

I dunno, it makes sense in my head. Of course... ideas are easy and quite often incomplete. Maybe I've just described carpel tunnel in keychain form.