I serve my feeders wet. Maybe that will keep more heat.
I also feed in the dark using a green LED headlight.
In the past when switching from mice to rats I would thaw them together. I feel this really mixed the scent and helped in the switch. I've always had good luck doing that. Not that you are equipped to do that right now.
Does that pet store not carry frozen rats so you can buy a few at some point? Instead of having to get live.