I would ask the teacher to see the bully is served first - that way they will be seated and your child can sit somewhere else - would that work? I don't understand your system but was told the other day the he had an assigned table for his class. Alternatively if your child is confident enough tell him to say "get you hand out of my food" in a loud voice. We used to advise waitresses to do something similar when customers had roaming hands.
I am assuming you work or have younger kids so lunchtime visits aren't an option? I would also be concerned about the school's response to such an approach - would you like it if some other parent came into school to put the hard word on your child.
