But I don't want to mess with the awesome relationship we've forged this year at his new school. They are fantastic! It's the district not the school level that would fight me on this.
In this case don't involve the district, if possible. In my experience, if school is willing to do something nice for you, they will do almost anything you ask, but if the district authorities do not know about this -) Ask about the end of the year test, or they can give your DS pretests before each chapter they teach. If he excels the pretest, he can work independently and learn something new.