IF...BIG IF...someone is truly not wanting to do business with a gay marriage because of religious reasons (and not just because it disgusts you)...then for EVERY wedding you could put scriptures on the boxes the cakes come in...and when you take their order...you can remind them that sodomy is a sin...."would you like sprinkles? Have you ever read Romans 1? I can quote it and sodomy is a sin against God........what color do you want the letters?"
Until they are ready to accept the message, the message will fall on deaf ears. You know, the old you can lead a horse to water routine.
Too much salt and too much light can be corrosive and blinding.