In all seriousness, with Bernie posting North Korea-esque numbers in Vermont, I have to wonder how many people would write him in in November. It obviously wouldn't be enough to swing the state, but it could be enough to push Hillary under 60%.
It would be interesting to see if the Liberty Union Party picks him.
Rocky Anderson and the Justice Party have endorsed Sanders and the Justice Party was on the 2012 ballot in VT.
The last time the Vermont Progressive Party endorsed a presidential ticket was Nader/LaDuke 2000.
Any one pf those three could do it. I don't think that Bernie would win even if he was on the ballot by name. I don't think that he would encourage the efforts either. I'm not sure in Vermont requires the approval of the candidate for a party to nominate said candidate.