Recognize that whether or not a G-IEP is even a legally enforceable thing at all-- that's going to vary by state, and perhaps by local policy if your state is one that doesn't really recognize gifted children as officially having special needs educationally, which are handled under IEP's.

Other than that, aquinas has excellent advice, I think.

Consider, too, that what Dude mentions is likely to be a serious limitation to in-class enrichment/differentiation.

I had a child that hated artsy/craftsy "enrichment" as well. I feel your pain on this one.

Schrödinger's cat walks into a bar. And doesn't.