Passthrough compositing for mixed reality

I tested the passthrough sample to get started (https://github.com/oculus-samples/Unreal-PassthroughSample) and I would like to invert the torch level so that the torch shows the VR scene and the rest is hidden by the passthrough. 

I tried to set an overlay passthrough over the scene and apply a 0 opacity underlay passthrough on the surface of the torch cone. But If I set reconstructed overlay passthrough on the level blueprint, it looks like it renders always over the surface projected passthrough on the torch, even if it has a lower priority.

All the examples in the template seems to apply the passthrough in different geometries over the virtual scene, but never the opposite. Can I have a passthrough scene and choose a surface that only shows the VR scene?