Sometimes non-complient gifted kids take an interest in something they don't want to do when they realize they'll need it to do something else they do care about. If he loves science and wants to study science more fully, then perhaps you could use that love to spur him to take a (necessary) interest in maths. Showing him the calculations scientists do to study black holes and such might help. And maybe doing some of the "perfect" ratio, "Golden Mean" math that sculptors use might get him to math through his art? (I'm SOOOOO not an expert on this, so here's a link to give you an idea of what I'm thinking of:
http://www.miqel.com/fractals_math_patterns/visual-math-phi-golden.html .)
Also, I know what you mean about not wanting to become thought of as "one of those parents." We're nice people, right? And it's not that we think our kid is better than the other kids. Plus, as compliant people ourselves, we want to be the "good" school parents.
But my own personal take on that problem is this: I felt like I was presented with the choice to become "that parent" or to let my child become "that kid." I picked the former--doing so as gently and as non-confrontationally as I could--since I don't feel my son ought to have to bear the label of the latter. This is in no way a criticism of you or your choices; I'm a *firm* believer that we each have to thread our way through the educational system/this minefield in our own manner! But I also think the system generally forces us to make the choice between advocating and becoming "that parent" or letting the child suffer. I think there's a way to be as nice as you can possibly be about it, but also to advocate for your child. I think focusing on your child's needs in the conversation, rather than "bragging" about his gifts, helps (with attention paid to the needs of the teacher and that particular classroom, too). You may still wind up branded as "that parent," but if you do, then there wasn't much you could have done to prevent that while still looking out for your child.
But like I said, we all have to figure out how to balance our children's interests with maintaining the attention of the educators and administrators, and we all have to do it in our own ways. I'm certainly still trying to figure out how to handle those difficult conversations, and I'm sure I'm not good at it!
Best,
K-
