Better:
“Why yes, I’m more than happy to (insert name of service/product to be provided at a gay wedding) for your wedding! And are you aware that for weddings of this type 100% of my profits are donated to (insert name of Christian gay conversion therapy offeror)?”
The problem will immediately take care of itself, without the Christian business having to either provide the service OR put itself into legal jeopardy.
The gay couple goes away angry, of their own accord, without anything they can do about it.