I'm afraid my experience isn't immediately helpful, but I hope I can give you some hope. My older son was very similar to yours in elementary. My younger son is athletic and spends any free time playing sports, watching ESPN, organizing his fantasy football, or playing his Xbox sports, etc (my oldest does play Civilization on Xbox... right, that fits, doesn't it).
Yes, it has been much easier for my younger one in terms of fitting in. BUT, I personally don't feel like more sports would have changed anything for older ds(actually, in addition to martial arts, he did soccer for 6 years, but he wasn't particularly good and he didn't love it). It took a while, but he eventually found his niche. For him, it was running (I was shocked to find out he was good at it, since he was slow, awkward, and ungainly in elementary), music (another shocker, but we found an instrument he loves), and typical stuff for gifted like math and chess.
One thing that did help him relate to other boys, at least on an everyday level, was reading about sports. In fact, it's one of the reasons we keep a newspaper subscription (we also did SI Kids). He enjoys talking to dh and his brother and I think he knows that knowledge of sports is kind of a currency when talking to other guys. No, he doesn't particularly love playing or watching football or baseball, but he watches enough and reads enough to sound conversant. I get that this isn't going to cut it for a 7-year old, but it did help quite a bit as he got older (definitely by the time he was 10, kids were pretty chatty about college and professional sports and it helped him fit in).
Honestly, though, I wish I hadn't worried as much. By 6th grade, a lot of kids had dropped out of organized sports, or started specializing in one, and recess was no longer an option or an issue. My younger son usually played those recess pick-up games, but he would also happily sit out at times to play card games, or chat with friends. My older ds was/is happy with his own company, but if yours feels sad at being left out, I'd talk to the teacher and see if he or she can intervene. That's not uncommon at our school, even though the teachers aren't with the kids at recess (they talk to the monitors, assign recess "buddies," suggest other games, etc).
It can always be awkward or discouraging to feel like the odd one out, but I think your son will find his place eventually, and hopefully there are at least a few other boys who also aren't sports mad.
