that's surprising, robos love their wheels. Maybe he didn't have one at the pet store... Maybe he's using it when you sleep? You can put some bedding on top to see if it's been turning... You can try the flying saucer, though careful because robos literally fly from it because they go so fast, so make sure you have a good layer of bedding around.... You can always let him run in a bathtub with towels, but please do not use a hamster ball which are dangerous.
I hope you find a nice cage soon, good luck cage hunting
