You could use scissors in the mean time. First of all, get him used to seeing the clippers, rubbing them all over his ear and around his ear. He probably had a bad experience with them, and needs to get used to the sight of them. Then turn them on near him. Put the clippers in your hand with them on and put your hand on his ear, which provides a gentle vibration. Then take your hand away and set the vibrating clippers against his ear. Good luck!
“Good things come to those who wait… greater things come to those who get off their ass and do anything to make it happen.” - Unknown