Is the idea that they would run as male-female teams, or is the idea that you would have a male-only candidates' race and then a separate female-only candidates' race? Those are the only two alternatives I can think of that would actually guarantee you'd have an outcome where there's one female and one male candidate. There's no way of doing it otherwise, at least that I can think of.
On September 21st, 2016. See this statement in context.