At this point, I really think you're going to have to wait until school starts and the teachers meet your son. Do they have assessments before school starts, or do they do them the first week? At that point, it will become really obvious to the teachers that your son is different than the rest of the kindergarteners. I think after the first week of school, you might want to set up a meeting and discuss his needs then. Perhaps you could even discuss a skip into 1st grade-- that happened with one of my childrens' friends. But in my experience, if teachers know your child, they're more willing to listen.
Two of my three are PG and neither of their K teachers wanted to hear about what they could do. With my son, who is now 10, the teacher's eyes about popped out of her head once she finished the assessment the week before school started. When she returned him to me, she said she would be looking for different materials for him before the year started. With my dd and a different teacher, the teacher had her read what my dd called "baby books," with all the other kids for about a month. My dd was incensed, and finally told the teacher the books were things babies "like 2-year-olds!" could read. Since virtually no one in the class could read the "baby" books, the teacher wisely gave my dd appropriate reading material from then on. In both cases, the teachers are huge champions of my kids now because they "discovered" their abilities (actually, it's probably also because they're wonderful teachers.)
If your son is still underchallenged after a few months of K, that's a different story and after that, you would want to start strongly advocating for him. But I would give it a little time.
