Rendering to offscreen buffer of a different size than render window

I have an odd stereo rendering pipeline where I need to pass left and right images rendered at 2K to a weaver object, and then display the weaver output at 4K. Thus I want my final render window to be 4K in size, but I want to utilize offscreen rendering to create two 2K images.

Currently it seems like the offscreen buffer is always the same size as the render window. If I want my offscreen buffers to be rendered correct at 2K, I have to set the size of my render window to 2K. But then I end up only being able to see a quarter of the final image that I want. Similarly, if I keep my render window at 4K, I have not figured out how to properly render my left/right images at 2K rather than 4K.

Is there a way to define the size of the render output besides setting the size of the render window?

Thank you

Just wanted to bump this topic up and see if anyone has any thoughts.