Something I posted elsewhere:
If you’re going to do this, you need some extra hardware. External interface to hit the start button on both games simultaneously. Probably also want an external (protected switch) to slam tilt both games as a reset. Serial output from game to report all score changes (even when DMD is showing animations). Potentially a computer/device monitoring the output and showing some sort of meter visible to both players as to who’s closest to winning. And the computer decides who has won — stopping the clock and showing the winner.
Recent Stern games have a serial port. If they could update code to dump information out that port during game play (timestamped game events including score changes), then other people could take up the torch of grabbing that input from head-to-head games and doing something with it (status display, declaring a winner).
You could also decide on how close scores are to declare a tie. The sport of fencing considers two hits within 40ms of each other as a double hit (otherwise the first hit locks out the second fencer’s hit).