Missile Command (trackball game) has three buttons to the left of the TB.
Wasn't a couple all button games with six buttons: left, right and reverse on the left side, fire and thrust to the right side, and hyperspace in the middle? You could do a three left and three right button arangement. That's what I have on my "test" trackball CP, all painted and, um, still in "testing" phase. Not sure when the non-test TB cp will be made...