You just have to try and hope!
Heat the rat with a hairdryer or heat pad to get it its body temperature to around 100 F, as if it were alive.
Offer by holding it by the scruff of the neck with your tongs, and point it nose first at your BP if she seems interested.
Do not wiggle or move it too much, or it might scare the snake, just a little bit at a time to look "alive".