I'm new to bp's too and transitioned from mice to rats seamlessly (he's a pig), but I've seen threads where people have taken rats and scented them by keeping them next to mice and gotten them to eat rats that way.

How long are you waiting between feeds? If there are no options you can feed mice, but it's going to be a pain for you.
I'm sure others with more experience will chime in & offer tips, but hopefully you can move to rats and feed just one appropriately sized rat per feeding.