Ask the teachers if there are some second grade lessons or workbooks from a curriculum that is not currently being used in your son's school. By giving him assistance in using those activities, your son could have some more challenging work to do while not running the risk of making him repeat the same things next year. You and the teachers could also search for software programs that would challenge your son in reading and in math, which he could do while the other children are doing the standard first-grade lesson.
Unless they are extremely gifted (five or six years or more ahead of their classmates), it does not benefit a child in the long run to let him or her skip a grade. Almost all children are better off staying with their same-age peers who are on the same level developmentally, rather than being placed with children who are older.
You may also want to lobby with the principal and the school system's central office to increase the time that the teacher of gifted children is able to work with the first-graders.