Probably not with an ipac. That effectively IS a keyboard.
You might be able to hack a wireless keyboard, but that could get tricky, and from what I understand, there can be problems with pressing multiple keys at the same time, etc with the keyboard hack approach.
However, there are tons of wireless game controllers on the market that people have hacked this way. Essentially, you connect up your buttons (and joystick switches) to the pads on the game controller board with a little soldering, and you're done.
If you want 2 players, you'd have to use 2 game controllers.