What about hand and arm gestures? ((I'm being serious here!))
You could practice with him some 'commonly used' commands and come up with some basics.
I'm thinking of ADD (not ADHD) as 'the ability to take in new information from the enviornment is taking a brief vacation' several times a day (or hour.)
There is a program where they teach children to monitor how 'alert' they are, probably by lifting their hands high above their heads to signify 'bouncing off the wall'
down by the ankles to signify 'couch potato' and face height to signify 'ready to interact.'
then you can praise the child for self monitoring and teach stratagies (running in place) to raise pulse and blood pressure when they are 'too low.'
I wish I could remember the name of the program, it was something like 'how does your engine run?' Does this sound familiar to anyone?
I just like the idea that on can teach a child to self monitor this important skill and then stratagise about it. Just to see, I would try a few compliments like: I could tell that your mind was really far away, but you were kind enough to come back to listen to me - good job.
Smiles,
Grinity