Could you try a clear ball he can run about in? I know you said he doesn't take too well to his red one, so a clear one might be worth a try. I will be another one to suggest getting another wheel. If you lived closer, I have a few wheels big enough for a gerbil that I would be happy to part with. Gosh, I hate how I am always hours away from people I could easily help out.
Good luck with his weight loss program. :]