Just have both of them run, while having their opposite number on the VP ticket during the primary. They can agree to have the one with the smaller numbers drop out and give their voters to whoever has a better campaign between them. This way, we get “Must vote for white dude” votes and “we need younger leader” votes.

There is no bloody reason for them to play by “traditional” rules, seeing as how the DNC and GOP don’t give a damn about fair play.