Get him on rat pups a.s.a.p cause some balls can be difficult to switch over. The sooner the better. The way you could go about doing it is with scenting the rats in mice. Or Chicken broth has worked in the past for me. My ball was a fiend so i've never experienced real problems with him he's usually been a great eater. Your ball should be able to take a rat pup though. Just remember The thickest part of the Pythons girth should equal the size of prey being fed to him. Best of luck switching.
Andrew