That's an interesting question, and I'll be interested to see what responses you get.

I'm pretty sure I remember reading that king snakes have the ability to sort of fold a snake that they eat into their stomach. Even if true, I don't know how much that would carry over to other species.

However, it seems to me that if you feed 2 mice that add up to the same weight as a rat that is the proper sized meal, that those 2 mice aren't going to sit nose to tail in the stomach. I'm sure there would be at least some overlapping, which would allow the stomach's ability to stretch in diameter to come in to play, so I think it would work out ok.

I regularly feed 3 or sometimes 4 mice to my bigger females, and it does not seem to cause any issues.