Well, if disgruntled Republicans want a third party alternative,

[Bluenorthwest]

13. Just responding to what you typed 'There are already third parties on the left' which

is followed with 'On the other hand, the right might have more success with a third party.' This implies that there are third Parties on the left and not the right. It is just not the way it is.
In 2000, Constitution Party and the Reform Party had candidates. Reform was Perot's Party.
The Third Party Candidates who got the most electoral votes were right wing, (Strom Thurmond with 39 , George Wallace got 46. On the left? Perhaps one once, or not, can't recall. 39 and 46 the GOP lost. Us? One, perhaps. )
So there are already 3d Parties on the right, as well as a much stronger history on their side of 'defecting' to such Parties. The only County that Perot took was Trinity, CA, which is nearly pure GOP. He was also one of theirs.
Your comments on the Greens are for another discussion, as that is a huge area of interest for me, the people I can win to go Democratic come from the Greens and the others on that side of things, the Greens were important to our winning Oregon in 08, primary and general. Green Dog Democrats we had. I watched Mrs O happily campaign directly to such Greens. .
I think for most of us, 2012 is now, and when we speak of trends that might grow out of this cycle, we are not speaking of a Third Party for this election. It is a longer game. If they splinter, we can either go more 'my way' or we can make a less 'moderate' Party and a 'centrist' one for those who want to stay close to the right wing. Not this year, as time goes on.....
I see their Party as far more splintered than ours, and the right as far more splintered than the 'left'. History shows that this is a long term trend. How we go forward on our side as they spin off and get weaker at the core is an important area of discussion, Party wise.
The right can mount and promote a 3d Party run quickly, and they do so rather often, actually. This is part of why they constructed 'Tea Party' inside the GOP. To allow a facade of 3d Partyism within the GOP. To keep those they know will easily go elsewhere.

Editing to add that I agree with your OP. This is just detail work, and the details I am offering suggest that what you hope for in the OP is not out of the question at all. In fact it is as likely as not.