I am a vet tech and ivermectin is useful for all types of mites, and so cheap it would be worth it to me to try it, esp since it should be safe for my snake. Oral is how I would go, as that way the mites cannot hide. I presume even putting it on the back of the head they still groom and get internally. Another thing, mites eggs are not killed with ivermectin, so it would need to be repeated maybe twice I assume. I hope someone more versed on this will pipe in.
*Fila*