Here's an odd thought that might hold up in court on l'affair Indiana. The new law prohibits discrimination on the basis of sexual orientation. One could note that objection to same-sex marriage need not be based on the sexual activities of the couple in question.
Two heterosexual buddies could marry, but such a marriage would be making a mockery of traditional values. Florists don't generally check for the sex lives of their customers, nor would a baker be checking for the orientation of customers getting a dozen donuts. Photographers doing senior pictures wouldn't care about who the teenager is sleeping with.
They might have a problem with being part of a wedding that doesn't fit the conventional paradigm of their faith.
Let's say that Kate and Allie from the old sitcom opted to get married in order to get the stay-at-home one and her kids on to the other's health insurance at work. As far as I know, that relationship was platonic. However, that marriage would still be one that old-school folks would be less than comfortable with.
There aren't too many cases of anti-gay discrimination towards customers that I know off, since it isn't an issue in most settings other than some get-a-room displays of affection causing friction. It's weddings that create the major legal issues, and one could make the case that issue from the old-school folks is of the wedding proper, not what will happen on the honeymoon.
Yes, 90-some percent of folk's issue with same-sex marriage is driven by the issue of homosexual behavior. But the two can be decoupled without Jim Crow 2.0 being created.