QS, I remember you posting about your ds a while back, sorry things have not got better....
It is really hard when a lot of boys in a class are into football - it can really take over and make the ones who are not good at it/not interested feel bad about themselves.
My ds1 (8) tried football briefly but got discouraged when the better players said mean things - I think often the coaches (here anyway) are quite young and not experienced at dealing with children and don't clamp down on this sort of thing (as a class teacher would eg)
Ds2 on the other hand probably will be good at football - and is also very popular. Ds1 said recently (rather wistfully) that he thought ds2 was the most popular boy in his class and that he didn't think he would ever be as popular . Breaks your heart...
But it is actually consoling to see how different the two boys are - at least it means it is not down to my parenting!
I would say that ds1 still doesn't have a close friend but at least he is not getting picked on like your ds....
The things I would try are:
For birthday outings (or if you want to get him together with friends after school) try something different that none of the boys are likely to have a lot of experience of - eg we have done bowling and it was very gratifying that the footballers were not the ones with the best scores! We have also done one where they did a bit of hockey first and then went in a soft play area ( the choice was between football or hockey and ds1 chose wisely!)
Really encourage him with the things he is good at - ds1 is a good swimmer and it was great for him that he was one of the first in his class to go in the deep end at school swimming. An outside school activity where he can make other friends is also good - we found Cubs worked for ds1. He doesn't see these boys apart from at Cubs but it is a start...and as they are all from our neighbourhood, hopefully some of them will go to the same secondary school.
Do the local boys follow the English football clubs? Ds1 suddenly started to ask if he could collect Match Attax - because everyone else was according to him! (will explain if you don't know what they are) - so now although he doesn't want to play football he can join in with conversations about matches, league tables, players, etc.
Have you got any games like Wii, Playstation? Boys here are really into them so it is a popular thing to do if they come around. Having a DS is also de rigour...
Re musical instruments, how about getting him to learn a "cool" one like guitar or drums?
Sorry this is a bit long but throwing all my ideas at you!