Hi Luc, try this...
Get a container that he'll fit into with an opaque lid so it's dark inside the container. Cut an access hole in the top/lid and fill the container with paper towels. Drench the paper towels so that they are holding as much water as they can and so there's even a little water they can't soak up. Now put this "humid hide box" on the warm spot and he'll spend a few days straight in there when he's going into shed, if he's anything like my bp's. Mine shed in one piece when I do this method.
For getting rid of what's left on him now, try taking a pillow case and soak it in warm (not too hot) water. Put him in the bag and tie it off well. Leave the snake in the sack on the heat pad used to heat his enclosure. Keep him there for 20 - 30 minutes and he will have a good chance of finishing that shed.
Good luck and let us know how it goes.