I would tell the couple that only traditional Christian weddings are performed using a script that contains terms like man and woman husband and wife. The state can’t tell the minister what to say in the cerement. Don’t think that the gay couple would appreciate having assign genders to each other.
Christian pastors should start including a sermonette on sexual sin, per the Bible, as a matter of course in their marriage ceremonies. Fornication, pre-marital, adultery, and sodomy/lesbianism. It should be sop. Then, when the sodomites attempt to coerce the pastor into giving them “equal treatment”, the pastor can say with complete truthfulness, that it will include such. It wouldn’t harm the normal (heterosexual candidates, since these days that’s not a given) couples any, either.