There’s no law that says you have to use ‘dr’ or another title; and can instead go by Mr, if he wants.

It might also be possible to go by dr [first name], if that solves the question of gender affirmation. Might also be simpler/easier to get people to go along with it.

Also, I’d happily Knight him myself. There’s no law in America saying I can’t, either. so, there.