This is exactly the sort of thing civil disobedience is for. This is where it works and where it is needed. A well-planned, trained- and prepared-for violation of this law could be effective. It could also be a chance for Love Wins and Human Beans Together to demonstrate what Uncle Frank meant when he said, “We must meet one another doing good. … Do good: we will meet one another there.”
That would be a lovely thing: Christians and humanists joining hands to defy an unjust law. Not planning a symbolic protest where they each get x minutes at the podium, but directly breaking the local ordinance in question in the very act of following an ethical demand. Because whether your higher authority is Christian faith or secular ethical tradition, sometimes the law is just wrong.