If he's adamant that he doesn't want to graduate early (does he mean "early" or "earlier" by the way?) then homeschooling may be literally your only option.
He doesn't want to graduate either early or earlier. If he were to stay at this school, my plan was to homeschool him for three subjects for the next two years (the school would give him high school credit for all courses taken including the homeschooled ones even though he would be registered as a middle schooler). It's complicated, but the upshot is that it would enable him to graduate with his age peers while still moving forward academically (at least in theory).
That the school is supportive of his two skips and the homeschooling/independent study piece is remarkable. I realize that it is highly unusual to find such flexibility.
