if you do mame it, mameplus has a head-to-head cocktail mode that works for horizontal games. The split screen may not be to your taste though, although I guess in that case one could always lay a divider across the screen. Anyway it's a way to get more simultaneous 2p games on a vertical cocktail... wish there were more of those in arcade history, but all I can really think of is the Atari sports games, Demolition Derby sort of, that multiplayer tank thing, and the Space Invaders cocktail ripoff where you both have a gun.