One of the best things we ever did was buy and install a meter on the TV, for 100 yen ($1) you could watch TV for an hour. From the time the girls were in elementary school we gave them each 300 yen a week allowance.
At first they popped it into the TV and watched TV, then they would coordinate between them to watch shows they wanted to watch together, then eventually they figured out it was more fun to go to the library and get 10 books each, sometimes twice a week, and keep the money for themselves.
Sure they both now have iPads and iPhones and they use them, but they also cherish going out with friends and interacting. I love the technology, we get to keep in touch with our girls in Canada, we Skype weekly, sometimes the family conversation goes on for 4 or 5 hours! :O we often eat a meal together over Skype, it is fun.
I don't have an answer for you Frank, sorry but maybe the idea of doing some cool stuff out in the yard would be good, but I bet, knowing your son a little bit via FaceBook, anything really fun, stuff that goes bang or BOOM would be out of the question, right? How about a pellet gun? Shoot some targets? Get the girls involved too, and some cooking, my daughters LOVE to cook, and bake, and they are very good at it too.
Best of luck!