If my school would allow a gifted IEP I would ask for :
"curricula compacting" - that is, he pretests math units and only has to join the class when the teacher is presenting the topics he did already knows. A book called teaching Gifted kids in the regular classroom has lots more examples.
Not to use all the "freed up" time for remediating strengths, but to allow "in-depth" pursuit of topics of interest. Your child also deserves an audience for his findings. Renzulli's school wide enrichment model has a lot to say on this.
And, why not be objective driven? First you'll have to test where, exactly, he is, and then say that he should be one year more advanced every year, yes?
Best Wishes,
Trinity
