I don't know if you can pick up an old dance mat controller on the cheap, or even if they'd interface with whatever gaming rig your friend has, but those feature face buttons and dpad as nice big squares you can "press" with your feet. Might be able to get some gaming done with that setup without breaking the bank.

Edit: searching around it seems like there's a good variety of modern dance mat controllers available. Some on the order of £10 if you're happy with a questionable quality aliexpress one, or more like £30-50 if you want something with more reputation. Could be a good solution if you want to avoid the ~$250 entry cost that other folks were talking about.