How do you help your ADHD or bipolar child socially?

My son is in cub scouts, but he has a difficult time keeping it together emotionally during meetings.  My husband and I are den leader and cubmaster--we have a weak school district with few parents in a position to volunteer.  It's almost too much stimulation for him--the excitement of a meeting or camping event.  His meltdowns make scenes.  We don't have another den to move him to and we don't have any other parents willing to step up and volunteer.

Sam has few friends left in the neighborhood.  Some of this is the season--it's winter and very few kids are out.  But there are other kids that don't come over anymore.  Some of it is that they are too old, some kids are over-obligated to other afterschool events, etc.  And referenced in another post, he had a nice friendship with a child 2 years younger that he screwed up by deciding to play and taking his clothes off.  The boy's parents thought it was innocent, so they said, but they haven't been showing signs of getting the kids back together to play.

Sam is shy at school.  Kids will talk to him, but he often won't return even a "hello".  I can't tell you how often we've tried to work with him on this.  We've signed him up for sports--mostly for some exposure--he's not very athletic.  He belongs to a "Kids Care Club" after school which he loves.  He seems to either play alone on the recess yard or get into trouble.  Occasionally, I hear he was included.

Sam goes from being shy to overbearing and obnoxious.  He's working with a social worker at school.  The psychiatrist hasn't recommended any therapy and treats my husband and I like we aren't doing enough for him. 

I don't know what more we could do.  Sam is having a birthday sleepover in a couple of weeks.  It's supposed to be just 3 or 4 boys.  I'm afraid none may show.  I'm out of ideas to help him.  My husband feels it's Sam's problem to work out--he has social problems and makes poor decision on how to treat friends.  I still think we have to keep trying to help him find his place--after all he's just 7.

Any ideas?

Mary