I think this is one situation where it can pay to go full retard. I was bullied loads at school, in years 7-8, particularly in that most favoured of bully's territory, the PE changing rooms. I put up with it for ~a year and half and then one day just snapped. Can't remember exactly what happened, but I ended up putting one kid's head through a wall, smacked another one round the head with a metal chair and got dragged off another one by the teacher while trying to impale his eye on a coat hook. Surprisingly enough they never touched me after that! Fortunately the school was aware of the bullying, so although I got a good telling off, they were relatively understanding.
I was lucky to be big enough to stand up for myself however, so if your nephew isn't particularly big, this probably won't work.
Also, there's the potential to get into a lot of trouble, if the school aren't aware of the current situation, and there's also the fact that this was ~15 years ago. Kids these days might carry knives etc, so it could make things a lot worse!