I have found through the 50 odd years that I've owned snakes that if you spray them down very heavily 3 times in a 10 minute period you can go back to the snake after that 10 minutes and peel the skin off very easily. I have found that soaking them in a tub will usually soften up the belly and side of the snake, but because the snake is buoyant the dorsal area is still pretty dry.
Another technique is to go ahead and spray down the snake 3 times in a 10 minute period then place the wet snake into a warm wet pillow case. Keep the snake in the bag for about 5 minutes, the friction from the snake moving around in the cloth bag along with the moist softened skin will usually produce a fully shed snake. This technique works very well for retained eye caps.
If you have any questions about snake husbandry, breeding or mite control feel free to call me at 408-981-6694.
Best of luck.
Brian Gundy
For Goodness Snakes