Here's a thought chain.
Colbert the flesh and blood man is a Democrat; he'll run his satire/protest candidacy as a Republican so he can mess with Republicans.
Liberal young Republicans who enjoy Colbert's show are probably, in a three way Giuliani, Thompson and Romney race in South Carolina, inclined to support Giuliani.
Giuliani can win a three way race if he gets some national security evangelicals and most of the social moderates, assuming conservatives split between Romney and Thompson.
If Colbert picks off a point or two, it's not hard to conclude that it'll come from Giuliani's tallies.
Although, just having written that, Colbert could siphon support from Ron Paul's crowd.