Forgot to add this: of course doing this necessarily lessens the honesty of the transaction, but I think that is fallout that cannot be avoided. Unfortunate, but a societal consequence of the feds regulating everything in sight...
Think outside the box.
What the homosexuals are doing is bullying and using the law to blackmail the photographer into taking pictures.
So ... get some friends and picket the event with signs that say “bully” and “blackmailers inside”. If they have a “just married” signed car, take water soluble paint and spray pain “bullys” and “blackmailers” onto their car.
You are not picketing them for being “gay”, but for their bullying behavior. Looks legal to me.