There are already 50 or more “third parties”, so that isn’t the answer.
Perhaps we need to form a coalition of voters who vote republican, who are willing to “boycott the republican party” in a formal way, a pledge that we are fed up and will refuse to vote for X.
Romney got this in real life in 2012, Cochran in Mississippi faced such a thing, if formalized, we could have a threat that would finally break the GOP open.
We need something that is for sure.