I don't know if this helps anyone; but, I needed a modified version of retrogame because I don't have enough buttons for some emulators (4 per player, plus 2 for coin/start). So I needed to be able to use combinations of buttons to output extra key_presses. I edited the retrogame code to support up to 6 combinations + the 'Vulcan Pinch' (same thing). Then I also gave them priority over regular key presses, so you won't get a combination of key presses.

The code is located here if you want to grab it and compile it for yourself.

I am in no way affiliated with adafruit, nor is this an 'official' release by the PiPlay team. But if you get a chance, you should check out Adafruit.com. They have some great stuff.