As far as I can tell, there isn’t a way to display two independent camera views / players (one in VR, one on the computer screen) currently in stock UE4, but you can in Unity.
You potentially could run two instances of a game where one is in VR mode, the other uses the screen, and they are networked together, but that’s kind of a crazy solution to the problem.
I hope we get a native way to do this soon, because asymmetric VR games are awesome and it’d be great to be able to build them in UE4!