J.M.
I would suggest giving him something to play with or just make silly faces at him to keep him distracted! I know thats what the other moms are saying but I also wanted to suggest using your leg to hold him down. If he is laying on the floor between your legs, if you swing one leg up over his body across his mid section, it would help hold down his hands for you. If he gets them pried out then he probably couldn't reach his private area anyhow (longer distance reaching over your legs). I almost forgot that one of my sister's friends had to resort to that for difficult changes and I have had to use that technique once or twice myself. Good Luck