But if you don't have a choice, this is what I suggest, something I've used untill I bought me a few USB joypads:
One player should use WASD buttons for control stick, F as L button, H as START, OKL: as C buttons, J as R, "," and "." as A and B and SPACE as Z.
The other player should use keyboard errow buttons as the control stick, 0 (numpad) as Z, 2 and 3 as A and B, 8456 as C buttons, 7 and 9 as L and R and ENTER as START.
It's easy to use since it's alike to the N64 joystick buttons.