Hi T.,
I'm going to be blunt and truly mean this to be constructive.
Peer pressure is the kind of evil that gets swept under the rug by most adults. At school, I am talking specifically about teachers as they are the only ones that CAN witness it. (I'm not saying that teachers are bad, please don't take offense. Teachers are paid to teach.)They are also not the child's parent and God is not holding them accountable to what happens to these kids. God holds the parent accountable.
You said it, it can't be ignored. I think you need to hit this issue head on. I don't think you really have any other choice. It really sounds like you have done everything right with your child. You can't WAIT and HOPE that he doesn't mess up or feel uncomfortable. What if one of the "good kids" falls in with the wrong crowd? That multiplies the peer pressure.
I would address it with the teachers, the principal and any parents that are willing to listen. Don't worry about embarrassing him. If he's as good a kid as he sounds, he'll get over it. He has plenty of time to fight life's battles. There are plenty of other things that build character.
T., you said you were open to suggestions. That's all this is. I wish you well!
God bless!
M.