This really applies to existing candidates switching to a new third party or non affiliated ticket. Due to ballot access, the Libertarians and Greens both have access in at least 30 States each. A candidate could unify with one of those parties (D or R facing it). It may not be the specific candidate one wants, but it would provide an alternative to D's or R's who don't feel represented.
If, for example, a candidate decides to run independent as a disruptive candidate, they could probably get on the ballot in a half dozen states, enough to split the party vote enough but not provide a viable alternative in the electoral college.