I've heard crazier theories.
Unfortunately, the last real stalking horse...there hasn't really been one, has there, in the modern (post-1968) era? It's not even in Taegan Goddard's dictionary. A stalking horse was a candidate who intended to raise some support, but then bow out in favor of a stronger candidate (who didn't want to enter as an active candidate yet, but also didn't want to see his potential supporters pledge to other candidates). Once all candidates had to run in primaries and caucuses, a traditional stalking horse strategy was no longer viable. However, it is possible to imagine a candidate who wanted to avoid running during most of the invisible primary period but didn't want his or her potential staff and supporters to disperse to find the use of a stalking horse appealing. As for the horse (that is, the "active" candidate who intends to drop out), in the old days the reason to do it was to ally oneself with a potential nominee, and perhaps to increase name recognition for a future run (or, in the case of a machine situation, it might be someone in the machine who is asked to do it). It's not hard to imagine the advantages for Newt, who would be able to extent his run of pretending to be a presidential candidate without actually having to risk going before the voters and having the bubble permanently popped (it's always easy to find an excuse for dropping out pre-Iowa, probably pre-Ames).
I have no idea why Rick Perry isn't running. If he had started a full campaign back in November, after he was re-elected, wouldn't he be the favorite right now?