I always feed, and always have fed, my snakes in their cages. I have never had a problem with aggression associated with feeding. As far as feeding prekilled rats instead of live, why not? It is easy to do and less to worry about when compared to feeding live rats.

I would attempt to feed him a frozen/thawed just to see if he would take it. Unless you are breeding your own rats, feeding F/T would be cheaper and more convenient for you.

John