If you still want him on your shoulder but not nibbling, you have to stop him from the behaviors you do not like. EVERY TIME he starts the behavior, you stop him and give him something else to do. If that means dealing with the behavior 50 times a night, that is what you do. Persistent behavior modification means a well behaved bird.
Sunny Senegal likes to nibble my teeth. All I have to do is close my lips firmly and tell her NO, and she stops the behavior. I admit I do sometimes give her good from my lips, especially if I am introducing a new food. No saliva with the bite of food, however.