All one need to do is say that they do not wish to remove their shoes. We are not going to wrestle you for them. Don’t wish to take them off, then don’t! A bit of additional screening is all you will get, and that never really hurts anyone. It happens occasionally at my airport, and not just for medical reasons. Some people just don’t like taking their shoes off in public, but the TSA has a procedure in place for those folks as well and they can still board an airplane.