I would use an "approach and retreat" type tactic. Establish a baseline, something that he will allow you to do, but isn't extremely comfortable with. Start doing it, and keep it up until he stops fussing, then stop and pet him, rewarding his acceptance. (Acceptance = Lowering head, loose ears, soft eyes, licking/chewing lips, exhaling) Then try again. When he really accepts, say, a soft brush on his head without reacting, maybe progress to a dry sponge, and rub that all over his head. If he gets upset at all (even a slight raise in his head is a negative reaction), do the same approach and retreat. At this point, he understands the A&R, so that familiarity along with the nature of the exercise itself will help him to understand that the sponge won't grab him by the jugular.
A wet sponge may always give you a little trouble, since it creates a very odd sensation in a very sensitive, not to mention blind, area. When he's ready, start with the sponge barely damp. There's no need to drown him all at once
, and treat him just like it was a dry sponge, A&R if he isn't comfortable.
It takes a while, but it will truly fix the problem if done correctly. You can do this for anything that needs to be around his head, clippers, fly ointment, sunscreen. My sis QH sometimes decides that he doesn't like dewormer syringes, and this exercise gets the job done.