Phin, just get some paper towel and spray that with Reptile Relief and gently wipe down the snake to give it some relief now. It will kill most, if not all of the mites. However, it doesn't kill mite eggs, so it's good you got the P.A.M. on order.

When that arrives, remove the snake, the water dish and hides and lightly spray the substrate (it really doesn't take much - most people use too much). After it completely dries, replace the water dish and hides and put your snake back in the enclosure. He should be completely mite free in 24 hours and as long as you don't bring in more mites, will not have them return.

You can always re-treat after 30 days, just to "seal the deal".