If him having a flip phone instead of a smartphone is feasible, I think that's a great idea.
Another thing you/the caretaker(s) can do is pay him in cash. He can spend his cash on whatever he wants in the non-virtual world, but if he wants to spend online, he has to show the care takers what he wants, and the caretakers can either go, "no, you're not getting that," or "ok, I'll order that for you" and then he can reimburse the caretakers with his cash.