It's been a plan since Wilson's time. Find a GOPer with a huge ego. Have your supporters work back-channel cutouts to whisper sweet nothings in his ear about how he should really be the GOP's candidate; that he should run anyway if they reject him. Make sure he's got enough money. Launch and enjoy your plurality victory.
It works both ways. Ralph Nader, anyone? Don’t forget the Mother-Of-All Democrat vote stealers: George Wallace in 1968. Got Nixon elected.