Rule of thumb, don't ever feed anything bigger than the thickest part of your bp's body. Live hoppers are usually used to stimulate the babies feeding response since they hop around a lot, hence their name, so there is really no reason to use them if they are frozen in my opinion, unless your bp would refuse fuzzies.

It is very cute watching babies learn to feed. They are very uncoordinated at first lol. He will catch on. Sometimes it might help if you leave to f/t in the cage overnight, so he can go back at it later.

If your having issues of him swallowing the substraint, I would suggest switching to paper towels or newspaper until he gets a bit bigger, or permanently. I find paper towels much easier to clean up.