Display scaling for watching 2D view on main monitor without empty space while seeing full 3D SBS on virtual glasses

I have an external display with resolution of 3840x1080 (virtual glasses), and the main monitor is 5120 x 2880. I would like to use the external resolution 3840x1080 for mirroring, but this adds a lot of empty black space on top and below the view on the main monitor. How could I scale the view so that the height fits with the main monitor, meaning that half of the view would be outside the main monitor when the aspect ratio is preserved, while I would see the whole view on the external display? I think this would be the best approach to meet my current needs with the virtual glasses, more exactly see the 2D view (the other half of the side-by-side 3D image) on the main monitor while the virtual glasses would display the whole side-by-side 3D. Another option would be to use the virtual glasses without full mirroring, but somehow overlap the views partly. Thanks.