I would think that a talk with a principal or other long time administrator is in order. Ask them, "what have you done in the past with children like my son?" or "have you had children with this ability before and what did they do?". I know my kid's school was adamant about not skipping grades, and yet some kids did. Some successfully, some did not have a good fit a grade up. Each kid reacts differently to this. The school rejected any idea of doing grade up math, or going to the grade up classroom for math time. And yet some kids in the school did that, too. Generally very successfully. Their parents were persistent until it happened.
You are probably right that you need to make this no more work for the teacher, which means YOU probably need to do it. If you want it, you must be polite but persistent, and helpful. Be sure to ask that if your kid is doing advanced work (but does not skip a grade), ask what will happen when he's in the last grade at that school. will they get advanced work to him? Will he have to be transported to the other school to do the advanced work?
When possible, pass along the things your son has said about school - frame it as "he says the worksheets are boring, he says he already knows how to do all this" as opposed to "I see that my son is bored, I see that he knows this already".
