Gradeskip is one way to keep a 'fading into the background' kind of kid up against the proper 'background' - although I'm wondering if homeschooling his is a possibility. Keep reminding them that NWEA's MAP is all about figuring out what a child is ready to learn next, and keep asking them to place him with other kids of similar readiness levels - don't worry about the age of those other kids.
However, do you think that you would get a school district to agree to grade skip a child who they can't even accept to be gifted?