Ground Plane Shadow Catching

How can we render models out of Stager, along with their Abient Occlusion, Shadows, & Reflections, without rendering the background objects that "catch" them?

• Ground Plane shadows and reflections will not export with trasparency. This worked in Dimension.

• Ideal workflow would be to allow ANY object (like a wall) to act as a shadow catcher, similar to how 3D layers operate in After Effects.