If Huckabee plus Romney total a majority, even if Huckabee plus McCain would also total a majority, I would think Romney could prevent McCain from taking the nomination by offering Huckabee the #1 spot. Given that McCain is a back-stabbing traitor in addition to being a liberal, and given that Romney wouldn't be able to do much else useful with his delegates, I wonder if that might be a worthwhile strategy?
I don’t think Romney and McCain like each other much either, but McCain is much more of a statesman and could probably say and do the right things to build a working relationship with Romney - IF he wanted to. I doubt he would want (or need) to reach out to Romney and I can’t say if Romney would be interested. If the three of them get to the convention with a split vote and no clear winner we would likely see some interesting deals made.