I'd probably use a new rat personally. After you thaw it out completely, blast it with a hair dryer on the head to get it nice and warm for him. Sometimes I aim the dryer at the rat while dangling it towards the rack to get the warm rat smell 'a flowin' all in their tubs. Sometimes it takes a while to get them to switch, sometimes it's an easy switch. Each snake is different. I had success with one of my pains by doing a live, followed by a fresh killed, then next feeding started out with fresh killed, second helping was f/t (he was a mouser, so he took 2 mice in a single feeding).

Good luck!