My snake is a little over a year old and didn't eat pre-killed mice, so he's been eating live mice and then switched to rats. At first, he ate immediately so it wasn't a problem. Over the last few months he's become finicky and stopped eating right away. Since I don't want to leave the rats in the cage, this makes feeding him a pain.

Is it possible to switch to pre-killed food and how could I go about doing this?