I'm usually inclined to keep wounds clean and let nature take its course on minor injuries, but this is one that might call for a vet to put in a stitch or two - hard to say. I guess it depends on how much of the lip is hanging off or if its scabbing together well on its own. You might try that first-aid superglue stuff, of course being extremely careful to apply only a tiny bit and let it dry while you're holding the snake's mouth open (again maybe something best done by a vet).
Good luck,
Billy
