Can you try a different teacher?
Can you get the OT to work with him on his current material?
Can you get an article from the OT for the teacher?
Can you get the OT to reccomend a teacher?
Can you teach him yourself?
Can you email thoes well known pianists who have dyspraxia and have them send an email to the teacher?

LOL - Good Luck - I hope I hit the right question in all of that.
I wish I was as good at the follow through as I am at idea generation!
Cousin Trin

Coaching available, at SchoolSuccessSolutions.com