None.

Nate seems to be proposing their supporters marshall behind one of them:

Still, there are a lot of Iowans who like neither Mr. Paul nor Mr. Romney, both of whom may be close to maxing out on their support. Mr. Romney, for instance, drew the support of 20 percent of caucusgoers in Tuesday’s Public Policy Polling survey despite the fact that only 44 percent of voters take a favorable view of him. In a seven-candidate field, converting about half of those who like you into voters is a very high conversion rate. The flip side is that about two-thirds of the voters who are not currently supporting Mr. Romney have a negative view of him.

There are extremely strong incentives for supporters of Mrs. Bachmann, Mr. Santorum and Mr. Perry to behave tactically, throwing their weight behind whichever one appears to have the best chance of finishing in the top two. What that means is that if any of these candidates appear to have any momentum at all during the final week of the campaign, their support could grow quite quickly as other voters jump on the bandwagon.

Good point, and one reason Newt's lack of ground game may not be that big of death blow for him in Iowa.

The question for Iowa for this year in particular is how strong is the protest vote.  Many of the voters don't like any of the candidates passionately.  So some will just "throw away their vote" on the candidate closest to what they want in order to send a message to the higher ups.  Is this kind of protest sentiment strong enough numerically to counter some of the dynamics you mention?  Some think it might be.  Santorum winning a few districts is not out of the question.

There is also the issue that the caucus doesn't actually allocate the delegates.  That won't happen until June when the contest is basically over.  The more messy it becomes, the harder time the pundits will have saying just who won what.  If that is the case, candidates like Santorum and Bachmann and Perry might just be able to spin some kind of momentum out it, keeping them in the race longer, which would continue to keep Mitts' numbers down.