It's going to be done like any other major political change has happened, comfortably inside of that two-party system. You have to mobilize political pressure to effect the change at all, which is the same thing you'd need to do for success with a third-party strategy anyways.
But hey, please feel free to do what you want, a real libertarian third party is the progressives' wet dream right now.
And this is going to be done by voting for the lesser of two evils? Interesting.