Vote for the strongest conservative third party candidate available. Mitt Romney will never get a vote from me. Period.
Another vote that helps Obama ... but at least you'll feel good about yourself that you stood on principle.
Don't you see? Your conservative principles conflict and you are forced to choose which one to sacrifice. On the one hand, a vote for Romney -- who is certainly not a conservative Republican (and I agree with you!) -- does not comport with conservative ideals and the GOP needs to know that's not acceptable. On the other hand, a vote that effectively (if not efficiently) supports Obama's re-election is not a conservative position to hold either. It comes down to deciding which action you'll take is better for America and the Constitution, my friend.