Fred is definitely acting as a counterweight against any other staunch conservative entering the race or gaining traction. His lack of ambition notwithstanding, he's having a fascinating effect on the process. The longer he stays out, the more difficult it will be for him to make up lost ground. Yet the longer he hovers on the sidelines, the more damage he does to the guys swamped in the low teens. That leaves Rudy, and his friend John McCain.
Fred's semi-presence does help McCain, in a sense, but there's no way for him to destroy McCain's enemies without doing the same damage to McCain. Now, he could undo that damage by getting on board with McCain as his Veep. A McCain/Thompson ticket (which is quite possible, given their friendship) would scramble the numbers and have everyone recalibrating.
Ultimately, if Fred wrecks all of the other contenders, it will hand the nomination to Rudy. That is clear enough, and he could easily parlay that ability into a VP slot. If Fred wrecks most of the others, and jumps on board with McCain, it would be a tough fight against Rudy, but it's not impossible to beat him. McCain may be broadly hated, but there's a lot of love for Fred out there, and it may be enough to win the nomination.
Fred's certainly a potent factor in the race, but it seems to be as a kingmaker, not as the king. I wonder who he's actually angling to work for.
McCain is not broadly hated. His net positive/negatives both within the republican party, and with the overall public, is better than all but Rudy.
A core conservative group hates him. But that seems to be a group that also almost universally hates Rudy (I use hate as a shorthand). Would that core group pick Rudy over McCain? Hard to say. There are so few things McCain is hated for that Rudy doesn’t fully support.
I’m not selling McCain, but he’s actually a pretty popular figure for some reason. Gingrich, now there was a hated figure (and that was before he sold out our party to the environmentalists).
He is working for himself. All politicians do. As you say, he wins whether McCain or Rudy gets the nod. There is no reason to make a move. Politicians love it when they win through inaction or delay.