Displaying 3D SBS background in stereo camera render

Hi,

I have ready to use 3D SBS 180 animation from another software.

I’m trying to add 3D effects in blender for later to composite.
Which in this case is just a sphere wit glass shader and modified roughness.

I will render this with stereo rendering turned on, matching my original render parameters.
I would like for the background to show left side of the frame when _L camera renders, and right side when _R camera renders, see setup below:

Right now, I’m manually uncheck right or left camera in stereoscopy settings and plug corresponding background frame side and basically render this as two separate files for each of the eye.

Is there a way to know which camera is currently rendering and in turn change which background image is displayed?

Thanks fot the response in advance.
Please note, I’m not that advanced in blender.

This is an example SBS background I’m talking about:


source

This is the effect I going for:

Try crossing eyes to see the effect.