I honestly would try a live rat pup, I've found it to be easier to get a snake eating live rat pups to switch to pre-killed rat pups than it is to get a snake eating mouse hoppers to switch over to rats. But of course every BP is different.
Personally I would give live rat pups a shot then try mice. Chances are you might have to resort to live anyway so why have to switch prey as well if it isn't necessary.