Unite so-cons and libertarians?
You mean find a way that conservatives can convert libertarians to conservatism.
The GOP needs to nominate a conservative candidate, and the libertarians can just decide individually whether they prefer the democrat, the republican, or the libertarian candidate.
That's fine as long as we stop blaming Libertarians as "spoilers" when social conservative candidates lose races.
Like SoCons, libertarians have "must have" criteria.
And like SoCons, if they don't get their minimum needs met, they won't turn out. I believe it takes both factions to win, in spite of your take-it-or-leave-it pronouncement.
That doesn't build a coalition.