You could put a trackball in there, but it would have to be something like a Penny & Giles 2" trackball, they have a very small footprint. You could also hack up a MacAlly iBall and get it in there. You won't be playing Golden Tee with those trackballs, but they work well for games like missile command, centipede, etc. Or in place of a trackball you could also easily fit in a Oscar Model 3 spinner or a homemade one like theNasty's or the one erikruud made (tornado spinner would also fit).