If it is a defensive strike (quick strike, no coil and VERY quick recoil back to the original position) its a behavior that should be conditioned out. There is the occassional BP that is a snappy little bugger its entire life. Posters above me are correct though. Try a gental head tap with a snake hook if you have one, the washcloth idea seems good just make sure he dosent strike at it and get his teeth caught. (He'll spit it out eventually if he does).

Get some gloves. They have incredibly small teeth and the bites really arent too terrible. Gloves will let him learn that striking dosen't mean he gets put down. Keep handling sessions short and positive and hopefully you will see an improvement.