This would have been known ahead of time, right? If they think it helps to be listed twice, then why wouldn't Sanford, or any Republican in SC, get the endorsement of some other phony third party, or form one themselves? They could call it the Pro American Party, or the Freedom and Liberty Party, or some such, and knuckleheads in the booth who don't want to vote Republican might see that and vote for it.
I like to think that the number of people who might vote for a candidate listed twice, but not if they were listed once would be negligible, but in the days of Idiocracy, we can't guarantee that.