To get it out of the way first, this will not happen for the same reason that no primary challenge will materialize. If there were enough voters out there hot and bothered enough over civil liberties to make a convincing primary challenge, then we would probably already have more civil libertarians in positions of power.
That said, this is a clever idea. The absolute worst that can happen is that the least dissatisfying of all the Republicans wins, and there is no danger of destabilizing the Democratic party (for those who think that is a bad thing). As Friedersdorf argues, there's really only an upside here:
At this point, Obama is effectively going to run unopposed in the Democratic primary. He'll be the general election candidate regardless. A protest movement that used the GOP primary as its vehicle would, at worst, fizzle out with no real effect. If it succeeded in getting Johnson even a bit more attention, there would be two voices, Johnson and Ron Paul, speaking out in favor of shrinking the military, ending the drug war, and protecting civil liberties; they'd give voice to an actual marginalized constituency on the right that the left should want to see better represented; in the unlikely event that elevating Johnson succeeded wildly, and he won the GOP nomination, the left would have dodged the possibility of President Perry or Cain; Obama would be no less likely to win the general election; and to do so, he'd be forced to move toward the civil libertarians on issues like drugs, war, and homeland security policies, rather than moving right. Much the same logic applies to Roemer. Elevating him would inject into the campaign more talk about the capture of government by various moneyed special interests.This has an advantage over mounting a primary challenge in that there's no need to start from scratch. Candidates have already surfaced in the Republican primary who are well to the left of Obama in civil liberties. The hardest part is already done!
One disadvantage that Friedersdorf doesn't mention is that there are more races next November than just the presidential race. Voters have the most sway in local elections. If a Democrat switches to Republican on a pie-in-the-sky attempt to sway a national election, then she may lose the chance to vote in a Democrats-only race closer to home. Of course, no one's vote is going to make a difference, one's party identification can remain secret, and there's nothing to stop a RINO (really!) from campaigning for their favorite Democrats.
My favorite aspect of this stratagem is that if it became a habit, if enough people regularly switched parties every election cycle, then that would represent a real assault on the two party duopoly, which would benefit everyone.