Unfortunately if you call them a diff pair you will get the "tightly coupled" version of the diff pair (you can make them edge or broadside).
But you just want two equally matched 50 ohm lines and push your signal and its complement down each one and have them arrive at the receiver in unison? Simple, just set them up as a matched group (relative propagation delay). All the same benefits. You can add multiple nets to this group -- if they all need the same distance rule.