Aiming with 2 stickmen would be easy, just fire both of them at the mouse.
...ohhh, you meant for it to be a 2-player thing. That's not what STK2 is for, but maybe it could be controllable with other buttons (maybe t/f/g/h and the number pad?)
I would think more of using aiming crosshairs movable by different keys. STKM1 would be one crosshair and set of keys, STKM2 would me another, different crosshair and keys.