First off, it is great that he likes going to school and has fun there. After all, that is pretty important, especially at that age.
Does he have the same teacher this year as last? If not, might last year's teacher be able to talk to this year's teacher and advocate a bit? If he does have the same teacher, surely he/she would see he doesn't need another year of exactly the same thing.
Have you thought about quietly mentioning to the teacher that your DS already knows the alphabet and phonics?
One thing that worked for me when my DS was in preschool and the class was working on letters and also on learning to print their first and last names was asking if it would be possible for DS to learn to write other high-frequency words, like color words, number words, etc. That way the teacher didn't really have to go out of her way to accomodate my child, but my child was still getting something out of the activities.
