NOTHING, absolutely NOTHING, worked on Matilda until she got a bit older. The best option was to squeal "OW" and walk out of the room. Even though it didn't work then, if Matilda nips me by accident during play and I tell her "ow", she cowers and feels soooo guilty. hah
Your best bet is to keep him tired - walkies, play time with dogs you know are safe/vaccinated, etc, until he's older.
We did the same with Leroy and it works! If we are playing and he is biting a little too hard I let out a high pitched "ow!" and he stops and comes and licks my face