This is just an idea. I have never run into Constipation with a snake. I did bottle feed a puppy from birth recently and had constipation problems. The only thing that worked for her was mineral oil. It can be purchased at your local drug/ food market.
I would check with your vet to make sure that it is safe for snakes and the correct dose. You could open the snakes mouth and squirt some in, but I would give the correct dose to the food and then feed it. That would be the easiest way to get it into the snakes stomach.