After Todd lost his arm, he first got back into the game by modifying the machines he already had. It wasn’t hard: he simply drilled an extra hole in the right side of the box, added another button just above the existing one. By pulling the left-button wiring through the inside of the machine body to connect with the right side of the machine, Ballmer was able to control both flipper buttons with one hand; the trickiest part, says Todd, was getting his brain wired the same way.

Source: Pinball Wizard – Folks