Belive it or not I know of some guy who used to brag about his kid beating a speeding ticket becasue he was singled out from the crowd. A young kid driving a sports car.
Sounds kinda stupid but if your son can prove he was only doing the rate of traffic and prove he was singled out because he was young and driving a sports car registered out of state,<actually dont have to prove it but just raise enough of a question about it> it can be thrown out of court because of prejudice and profiling.<if you can, ask a Statey in New Jersey about this>.
That letter has as good as a chance as any, with only a bargaining plea of a non moving type violation, " I wasn't doing anything unsafe since I was doing the flow of traffic. I will pay the fine but please make it a non-moving violation" possibley having a better chance.
You have the cards out on the table which is already more than what the ticketing officer or the judge will expect. Good Luck!