Ahhh...sounds like he's had a rough go of it, and him being a difficult feeder makes a little more sense.

How exposed is his enclosure? Does it have a glass front that is opened to a well lit and/or busy room? Have you tried covering it and keeping it covered most of the time? That may help him feel more settled and secure...just a simple blanket or towel draped over the enclosure to give him darkness and privacy most of the time.

You may be trying to over complicate things. "Switching species" doesn't mean trying to find something exotic. Whatever you choose to feed him needs to be something readily available and affordable. Seriously...try a f/t mouse before you try a live rat. It's a simple solution with a high chance of success. If the mouse doesn't work, you haven't really lost anything, but if it DOES work, then you've found a simple solution that will be easy to continue working with.

Switching to live prey carries a different sort of risk. If you do choose to go that route, then I would highly recommend you get something small, like a baby rat that is just barely weaned, or not yet weaned. It will be too small to be a complete meal, but it also won't pose any risk of injury to a reluctant snake. If that turns out to be a success, you can gradually increase the size of the live rat as your snake gets used to eating them. A ball python that is anxious and eager to eat is in no danger from a live rat...but a shy, reluctant eater has more risks.

Never try to feed immediately after a failed attempt. Always give it a full week between tries. For whatever reason, your snake is feeling stressed about the encounter with the rodent, so repeated attempts too close together are counter productive.

Have you tried just laying the thawed/warmed rodent in the cage, covering the cage and leaving it completely alone for 24 hours? Might work. Rather than trying to get tricky with the "feeding tricks"....try to consider how to keep things as calm and stress-free for the snake as possible.

Good luck!!