I have delt with bullies in the past aswell. All i can say is the only way to end it is to gain their respect and the only way to get it is to take it. Bullies are cowards that is it so they pick on kids that are weak and have a low self esteem. Teachers and friends do not help because they will not be their all the time and the second they leave the kid will be open to get harassed. I ended my bullying by beatting the crap out of the bullies then they knew not to mess with me. Ironically I became friends with one of them for the next year of high school.
They need to get this kid to a Muay Thai or boxing gym PDQ (Pretty Damn Quick) and he needs to knock the shit out of the biggest bully he can find and gain respect of not just the bullies but the people around him.