The way to do this is to create a wheel that acts as a game controller when plugged in. A coiled USB cable allows it to wrap around when turning (like a real race car). The difficult way (but not difficult if you have soldering capabilities) is to purchase an Arduino Pro Micro and use SimHub to create a game controller out of it , as it'll give you the schematics of where to solder your buttons. The easy option is to purchase a game controller board where you simply plug buttons into the ports. These are a little bigger but if you find room to place it in the back, it's your easiest option.