Hello Amby. This does seem serious issue and which happens in most of the parts of the world.
PROBLEM: SIZE of the kid; Bullying; Kid is alone;
GOOD: This kid's parents are concerned
BAD: Other kids' parents are NOT
SOLUTION: Try to find some common sports between this kid and other kids.

For example: Soccer (WC14 is coming)

In soccer you have two teams, at least the half of the team will not be bullying him. He will be secured and at least feel that he is supported by his team mates. However, he should play and practice quite often. So, that he can show things off to others. In this way, he can be friends with his team mates and slowly other team kids will stop bullying thinking he's got his boys now.

OR

Choose do some other sports with other kids. But, here again, this kid should be good at it. And, while playing or hanging out with them, the KIDS who BULLY him should see him hanging around with these guys (and respecting him). Then I think it will automatically stop.

Amby, the bottom line is he should show ppl that he is not alone. He has other kids who support him.

I am not sure this is right or wrong. Just coming thoughts from my own childhood experience, where I had no strength to block these kids. However, I had HUGE support from my guys (LAST BENCH) although I was first BENCH guy. Nobody ever touched me or point a finger at me. Once a kid (from grade 4) did when I was in grade 5. Oh God, that kid got ram dhulai from my boys. He was absent for 1 and half month.

Anyways, Good Luck Amby !!