[Gear VR] Rendering UMG widget in StereoLayer component - how? (BP only)

I am failing to display anything in StereoLayer component, not even a simple texture is being rendered. Ultimately I'd like to have UMG widget there so that I could put various messages in front of player when needed.

Is it even possible? Can someone please show me how ?

Thanks

P.S. I hope it's not more "expensive" than having conventional 3D widget in front of the camera