Well, if you aren't ready to try live yet (though i do encourage it - especially rat pups, since they don't bite or chew like mice), then here's something you might try.

Feed at night time. Make sure the rat pup is thoroughly thawed. Then heat it up with a blow drier and use a temp gun to make sure he's about 100 degrees or warmer on the head. Put the rat pup in their den or hide and leave it over night. You can either have the BP out of it's hide, where he'll find the rat pup when he goes back in it later. Or you can gently lay the rat pup inside the opening with the BP already in it.

Bps are ambush hunters and the above will often work (and has often worked for me). So has putting a fresh killed or thawed pray and the snake together in a paper bag inside their tank...check in the morning, and the food is gone.

Also - if you haven't read this article - it's great. I wouldn't consider yours a "Problem Feeder" yet, but this offers some insights and temps that might be helpful...
http://jkrballstreetjournal.com/2014...-eating-again/