Question Rendering camera background image onto another camera

Out of interest, what is the best way to render the AR camera image onto another camera? The current ARCameraBackground component requires an ARCameraManager component to be on the same GameObject, and having two in one ARSessionOrigin can cause issues.

So was wondering the best/most efficient way to handle this? This is for a portal system we have setup, but to render the "real world" from inside the portal we need the camera image.