Make your own home made proventamite using nix shampoo. Like Zoe said let him soak for a bit in some of it.
Here's what I've done in the past.
Spray snake inside a rubbermaid. Take out all substrate from the cage. Spray down the cage then add new substrate (newspaper) and spray it again. If you hide boxes are plastic spray them down too. Put that snake back in the cage with out a water bowl for 24hrs. That's all there is too it. But the water bowl back in and go on with life. Repate the whole thing in 5-7 days just to make sure but one treatment is usually all it takes. If you suspect mites always look in the water bowl you'll find them dead in there if you have any.