Good luck to you! It sounds like you did a good job easing his system into the level of meds he needs. Most psychosis drugs require doses by adjustment. His little body probably couldn't handle the doses he was initially given, poor little guy.
I have a 7 yr old boy too. We don't spend alot of time indoors over the summer but when we do, I try to make our time fun.
We have Storycubes - dice looking things but with different symbols/pictures on them and you have to tell a story in they order they land. Its pretty cool.
Read together. I got a huge book of children's classic stories - Alice in Wonderland, Jungle Book, Treasure Island etc and even though he's an excellent reader, I still like to read these kinds of stories to him.
Blow up some balloons! He can get some excercise hitting one with his hand or tennis racket, or you guys can play a game of volleyball. My son likes to try and hit a balloon by throwing another balloon at it. Its very challenging...take my word for it :)
Look on the internet for basic tae kwon do or karate moves, and practice them.
Get a survival or outdoor book on how to tie different knots, like the boy scouts do. Or I'm sure you can look it up on the internet. Most of them will have step by step guides how to tie knots. You can use long rope or new round shoe strings. Knots are always fun to learn for boys.
I like to buy big packages of paper plates and straws, and give them to him with a roll of tape and see what kind of creation he comes up with.
Never underestimate the power of coloring at any age. Especially if you color a picture together - sort of like tag team where you draw one thing and then he adds on another and so on. Its fun and the picture you end up with might be really cute. Get some butcher paper and spread it out where you have room. Butcher paper is always fun to color on.