I don’t think they can throw someone in who hasn’t run in the primary I think one would HAVE to have SOME skin in the game, I could be wrong !!!
The Democrat and Republican parties are private organizations who make their own rules. I suppose some investigative reporter should find out for sure, though. I believe the Dems can and will continue to do whatever it takes to win, and get away with it, no matter what. After we saw Comey do what he did, nothing surprises me anymore.