If your husbandry's right on the dot, then you may just have one that refuses rats. Sometimes no matter what you do they just won't take it.

A month isn't terribly long for a BP but it's better that he eats than not. I'd just give in and give him a mouse if he'll take it--I'm also having a terrible time switching my girl over. She'll take jumbo mice no problem but won't take rats (brained, heated, scented, small, big, male, female, white, black, pink and purple polka dotted etc.) no matter what I do so I'm gonna continue offering but keep a steady supply of mice on hand.

My other one will eat anything I throw in front of him. Their personal preference I guess. =/

Good luck!