I think a write-in campaign could work. Only obstacle is the GOP holding Hillary over voter’s heads like they did Obama in 2012. Not sure we could educate enough that the choice of no-choice would be widely understood before the election.
But then when you look at Trump’s crowds and votes maybe we could.
We should be able to convince 33 Senators in the Senate to form a 3rd Party. That would be the quickest and most powerful way of doing it.