No one can force the photographer to work a wedding he doesn’t want to work. All he has to do is state a very high fee to be paid in advance. If the couple still want to hire the photographer, he should go for it.
A for the the cake baker, the cake should be baked and held for pick up, paid in advance. The cake baker does not need to know the details of the wedding, just what kind of cake and how it is to be decorated. Follow a don’t ask don’t tell policy, only one name appearing on the sales receipt, the person who will pay in advance.
That wouldn’t work. This is reminiscent of the 60s when people didn’t want to sell their homes to black people, so they would up the price when they would come to look at the house. But then either the black people or a black organization would send a white couple on the premise that they were interested in the house, and when the real price was quoted, the homeowners would be sued.
All a homo couple would have to do would be to send a non homo couple to inquire and find out the real prices and then sue the merchant.