I ask, why ask! I don't understand why your H has to have his limited position met.
Tell him "A" or "B" works at this stage of the pregnancy. The old way doesn’t. Tell him you need to have some sexual release to feel comfortable, to avoid feeling so uptight or what ever and the baby's position dictated he does you "A" or “B” style. Tell him because you two haven’t practiced that position you will both have to learn to do it or try something else, something similar.
Sometimes I am reminded of a mortician story (not nice) when I hear what your H will only do.
Sorry for being blunt, but trying to work through some of my own SSM with BB leaves me with a short fuse.
Hoping things go well with the delivery. It's different now, but back in the early 70's if the babie had all their working parts functioning properly, that was the first concern. The Boy/girl plumbing made less difference.