Tricks for switching from mice to rats.

[WesleyK]

So I was just wondering if anyone would share their tricks for switching to rats
I have a ball python and a boa, both of which can take rat pups.
But here are my issues.

The ball is still young and went on a hunger strike and ended up eating again on live. And I can't get him back to f/t yet and I don't want to buy a live rat pup and have him not eat it.

And the boa I just recently got from a rescue, he is about 2' and they were feeding him mouse hoppers by sticking him and the f/t mouse in a pillowcase and leaving till he ate.
So I know he still needs time to settle in but now he is in a nice home and I'm worried he is gonna be expected to be shoved in a bag to eat.

Any help is appreciated.