R.
S.,
What is your son interested in? Since those with Asperger's Syndrome seem to be focused on the few things they really like and enjoy, it would seem that you would need to find a summer camp, or a youth organization that is involved with the same things that he is, be it cars, astronomy, music, or chemistry. If he is with a group of kids his age interested in the things that he seems to focus on, he should find a connection with them to help develope social interactions. I'm sure there's one out there.
Best wishes.