Hi, J.-- I wish you lived closer so we could get our seven-year-old sons together! I really relate to a lot of what you describe, so please don't feel your child is some kind of odd-ball. It ripped me up last year when I asked my son what he did at recess and he said he kicked the frost off the curb by himself. He is settling in better now, but he is still selective in his peer interactions and learning to be less awkward. Here are a few things I've learned:
If the child is OK and not unhappy, then things are OK. It's important that I not try to project my own social anxieties onto my kid.
I have several friends who homeschool their children, and while my family does not homeschool full-time, I like to create an atmosphere of learning, so I've read a lot of homeschooling-angled books. One point that is often made is how unnatural it is to be in a large group of children who are all the same age. Some people believe this typical American classroom set-up is pretty much a bully factory. In a mixed-age setting, the older kids help the younger kids, but in a same-age group, children who are confident or dominant may take over and boss around the less-assertive children. This sounds like it may be happening with your son and some girls--second grade can be a time of major social development for girls especially. If he is a generally nice boy and doesn't tease or play rough and is good at imaginative game, he may fit right in to the girls' games and accidentally become a victim to their social games when things go sour. Just be sure he knows that while it's not OK to be unkind, he doesn't have to play with anyone if he doesn't want to, and he doesn't have to limit his friendships at someone else's request. He may also benefit from some time spent with older or younger children so he can teach younger ones how to do something and learn from older ones. Look for another family you can have family events with to appreciate the mixed-age group and build social skills and confidence.
I like the recommendation of Cub Scouts--that will be great when he turns 8, since that's when it starts. They do a lot of small building projects and crafts that your creative son may love. They also practice some public speaking skills by telling jokes and such.
My sons are enrolled in gymnastics classes and they love it. I love that my seven-year-old is in an all boys' class that is taught by a man, so he has a chance to be "one of the guys." He has enjoyed it so much, and it made me realize that nearly every other aspect of his life is run by uppity women! ;) I'm usually with him, his school and church teachers are women, his dance and swim teachers are women, and so on. His dad is his soccer coach and is a wonderful father, but it's good to know a few more guys, too. He loves gymnastics since it is more a competition with himself to do his best and improve; same with swimming and dance at this age. I figure, as an American male he's going to get a ton of competition introduced to him as he grows up, so there's no need for me to push it if it's not his thing just yet. Although--my son has loved AYSO soccer camps during the summer since the British (male) coaches are so fun and enthusiastic.
Finally, you might really appreciate the book "Hold on to Your Kids" by Dr. Gordon Neufeld. This book really reassured me. Neufeld talks about the all-too-common phenomenon of "peer orientation," when children and teens shut out all healthy adult role models and become fixated on their peer friends. It's common, but it's not healthy and leads to risk-taking behavior. That book helped me remember that it is OK for me to filter my child's social life a bit, and that he is so well-connected to his family that he has very little attachment energy left for peers he may simply not relate to just yet. . . and that's perfectly healthy, shows security and not an indication of social awkwardness in the future.
Perhaps your son would enjoy a play date with another boy if there was a project to do, instead of just free play? You could bake cookies or make paper airplanes or do a science kit together.
Consider having a family night with another family, so your child can play with another boy while both families are having a bbq. Having family around could help him stay comfortable and allow you to offer support as needed. Maybe some games or a fun project, like packing up a box to send to a soldier or hygiene kits for a homeless shelter. You could take your son shopping for the componants and then let him help explain to his friend and friend's family how to pack things up.
You are not overbearing or controlling--you sound wise and intuitive and loving. Best wishes!