If it were me ordered to bake cake and take pictures of gay unions, they would be unrecognizable. If they want nice pretend wedding pictures, best to pick a secular photographer and if they want a pretty “wedding” cake, best to choose a secular baker.
My response would be similar. I'm not one to fight losing battles. Fighting evil in court serves a purpose, but I am not the right person to do it; I would not refuse service. If artistic wedding support was the job I chose for my retirement, I also would not show up for the pretend ceremony. I would make sure the contract specified that there was no penalty for nonperformance, and I would cancel at the last minute. Thugs are entitled to neither honesty nor courtesy, so I would not even attempt to deal with gay demands for service in good faith.
Photography? After signing the contract, I would suggest that they hand out disposable cameras to the guests as an added fun activity (even perverts and bullies deserve some record of their faux-ceremony, just not my artistic talent or slave labor to create that record), and then I would call in sick an hour before the ceremony. If they were at all threatening on the phone, I would show up, swallow Ipecac on my way in, and leave after throwing up on the floor. "Sorry," a true statement, considering how sorry I am that freedom is dying, "I tried because you were so upset, but something made me sick, and I cannot do it."
Baking? Same thing. I actually do bake experiments before bringing anything to a party/gathering, and I would try an experiment before the "wedding". After tasting each part/layer, to learn how those recipes turned out I would assemble the cake, and then "trip" to either drop it or push it off the cart and dump it on the floor on the way in. Again, last minute, no proof of intent to refuse, and no artistic support for perversion.
Wedding venue? I would hire a friend with septic trucks to come and spend as many hours as necessary "pumping" back and forth for the duration. Or I would disconnect the wiring for the well pump and call another friend for service. "I've got a problem," and I do have a problem with involuntary servitude, "perhaps you could hold the 'ceremony' at the public park?"
Under no circumstances would I participate in celebrating perversion. If refusal is not permitted either, then I would go through the motions of compliance and then fail at the last minute in a manner that is not provably intentional and that the contract specifies cannot be penalized.