Player (First Person) have magic glass item (ring shape for example). Through the magic glass player can see hided objects (static mesh, skeletal mesh) on the level. Objects beyond the borders of the glass are invisible. Some pic:
Reminds me of a new mechanic in Dishonored 2. You have a kind of pocket watch and you can see an alternate timeline through it in real-time. Pretty neat feature.
I’ve actually just submitted something which might help with what you’re wanting to achieve.
It works reasonably well in VR but to get what you’re looking for, you would need to have two scenes with one showing the alternative view.
If you’d like, I can drop you a message when I know more about how the submission is going as this is something I’ve seen a number of people try to do with little success.