D.T.
You need to get him to a professional, someone who deal with children and OCD's. In adults I know they can be reasoned with, their minds can process that they don't really NEED to do their rituals. I am unsure how a 4 year old mind would handle this...it's like the difference in dealing with pain. Give an adult a shot and they sit and take a deep breath...try and give a child a shot and all hell breaks loose. An adult can deal a child can not.
If your child is OCD then you need GOOD outside help.