Calculus in 11th grade is already two grade levels ahead of normal math progression, although taking the slower calculus AB then BC route will end “only” one grade level ahead by high school graduation. It does not seem like a particularly high value idea to do a bunch of scheduling gymnastics to try to accelerate more. Completing multivariable calculus at a local college in 12th grade will advance him by only one more semester in math (and if the multivariable calculus course is only a high school course, it will not be given credit, so it will not advanced him at all).
Perhaps of more importance is for him to ensure that he is fully ready for whatever calculus he takes. rurci3 is a quiz that can help him check what he may need to review before taking calculus.