I agree with trying live for a few weeks. Small rats, make sure you are close enough to stop the rat from hurting him if he doesn't go for it immediately. It seems offering live triggers their hunting/feeding instinct. Any snake that has been traumatized by something is going to be difficult to feed. This may wake him back up.
Once you get him feeding regularly and get some weight on him, you can look into switching him back to f/t. I've seen many on here completely against feeding live, but in the case of an underfed animal... It should always be about what is best for the snake. <I'm a firm believer in the food chain... Snakes eat live mice/rats... End of story.>
best of luck, let us know how it goes.