I don’t think this is possible without modifying source code unfortunately, and I wouldn’t know where to begin. I’d search and see if people have been able to do “split screen” but on two monitors. nDisplay might also be an option, but I’m just brainstorming here.
I’m assuming that you’d like to use the 3rd person character BP for the player controlling the Spectator Mode Camera. You can’t use “Add Movement Input” without possessing the pawn, and since our player controller is possessing the VR Pawn, the workaround would be to use an AI Controller for the 3rd person character, and add the SceneCaptureComponent (just like in the example project) to it.