The vet we go to had to treat a red tail with a prolapse, and she also recommended a lukewarm sugar water bath, that is supposed to reduce the swelling.I remember seeing the red tail, not much larger than a hattchling, and had only been eating pink mice, which makes his situation unlikely to be large meals, and his prolaps stuck out about half the length of one of my fingers. He also needed surgery to tuck it all back in.
I have had luck with a prolapsed hemipene and water based lube (like you would use for probing) Alto keep it moist, and then put our boy in a very clean tub, changing paper towels out regularly.
Maybe you fan also discuss this with the vet, and your findings? Your vet may agree with some methods that may help the snake.