I think you might be forgetting just how many "mainstream" Republicans and Democrats could go for a Gary Johnson or Jesse Ventura Presidency. So much campaign funding will end up coming from these sources that, when inevitably the wheat is separated from the chaff, only the candidate(s) who really take root with the voters at large are left, and there won't be any more talk about "viability" as far as our pick(s) are concerned.
Let's face it; a lot of U.S. voters go into the thing with a "horse race" mentality. It's not about philosophy or the ideals of liberty and Constitutional government, it's about "picking a winner." If we can provide enough candidates to give them that feeling of choice and at the same time let them feel like they're picking a sharp guy, an up-and-comer who can win, their primitive psychology will do the rest of the work for us (the MSM does it all the time)!