Nice try. One state gives gay marriages, and all states would have to recognize those marriages. And employers would have to honor those spouse benefits.
So much for the rights of people in that no gay marriage state.
Funny how they want to leave this to the states to deal with...yet when it comes to abortion, it's a different story!
If such a situation threatens, you then advance a Constitutional Amendment that states that the Full Faith and Credit Clause will not include the definition of marriage and such an amendment will ratified in a heartbeat.
In the meantime, I would rather keep the subject of buggery out of the Constitution.