Was he tested privately or through the school? I'm guessing it was private testing, so fwiw you could ask the person who administered the test to either calculate FSIQ specifically for the school and/or write a brief letter to the school explaining what GAI is and why it's appropriate to use in place of FSIQ in this instance.
I also wouldn't be so sure the school district gifted staff isn't familiar with GAI - it's a fairly well-established measure and dips in either processing score or working memory aren't entirely unusual or uncommon among highly gifted kids. A classroom teacher might not be familiar with it, but someone somewhere on the g/t staff in the district should have heard of it
Best wishes,
polarbear
