Maybe try putting some rough (not sharp!) decor in the enclosure if there is none. That way the snake can rub on it to help remove skin. Some good examples are hides or water bowls made out of that kind of rock-like material and pieces of wood. Make sure to use things that are made specifically for reptiles or sanitize the objects well.
Thank you for saving him!! Terrible TERRIBLE that someone would just want to release him... especially at only 3 months old. It sounds like he probably didn't have the best care... you should consider bringing him to a vet just to give him a general check-up. The wrinkles you see could be from being under weight or dehydrated. Do you have any pics of him to share?
I'm so glad that he's in good hands now with people who truly care for him! Good luck with your baby!!