If you are going to homeschool under a school umbrella, all you should have to do is move him to the new school and have the new school request his records. We homeschooled under this exact scenario and no problems whatsoever. On our son's last day at the old school, we just went into the office and told the principal we were transferring him to such-and-such private school. The principal said, "No problem, the new school will write for his records."
“ISIS, Their days are numbered. I won’t tell them where and I won’t tell them how”.