Mirroring the view inside the HMD

I want to mirror an entire level. For my proposes it works fine in desktop mode by using a post-process material that mirrors the view. The blueprint example is provided here:

How to flip the camera display in the y axis to create a mirror world ?

However, while this material also mirrors view in the VR-headset, it mirrors it in a way that it doesn’t line up properly between the eyes, it’s a bit hard to describe, but maybe the stereoscopic view is gone or that the offset is wrong. Any suggestions to how to solve this problem?