I don't have a religious litmus test either, but I do worry what the media will do with the Mormon issue. I don't think it's something he can get past with a witticism. If the media decides it will be the single most important thing about his candidacy, then it will be.
I don't think it would be that big of an issue. I heard Glenn Beck ask Jerry Falwell (during an interview on Beck's TV show) if he could vote for a Mormon for President.
Falwell's answer was excellent, and he said he would not impose any "religious" litmus test on a candidate, his stand on issues and morality would be what he judged a candidate by.