The border shaders use the full 16:9 aspect ratio, as well, but they set their own aspect for the game image with the border around it. You could keep your aspect ratio at 16:9 and then switch between the border shader and cocktail table shader using the next/previous shader hotkeys.
Those hotkeys only work on presets that are in the top-level of your shader directory, so you’ll need to create some presets there that point to the shader files.