I was thinking along the same line
That's pretty crafty, since it's likely this provision would not stand against a legal challenge. A KofC hall is not, strictly speaking, a religious institution. If a hall owner rents for any wedding receptions other than those subsequent to a sacramental Catholic wedding, they'll be required to rent to any legally "married" couple. This obviously illegal provision of the pending law will be voided by the first court which hears the challenge.
Once the definition of "marriage" is broadened, a venue, like a KofC hall, by virtue of past SCOTUS rulings, must be made available to all (unless the owner decides to restrict rentals to sacramentally married Catholics) on an equal basis. Just as a wedding hall owner can't refuse to rent to a black or interracial married couple, the case will be made they can't refuse a gay couple's reception. KofC councils will be forced to get out of the wedding reception business, or restrict the rentals only to those sacramentally wedded.
However, I wonder if DOMA which does not recognize these marriages makes it different