Michael Booker: "Why I Don't Use Female Pronouns For My Transgender Brother"

This is exactly right, and I've made the same arguments before.
   But also: to use sex-specific pronouns incorrectly is to endorse a crackpot social constructionist metaphysics, in particular about sex/biology. I wouldn't make a federal case out of it...but no one can insist that you do it. Or, well...they can insist all they want...but you're under no obligation.