This isn't really possible to do in software. NVIDIA DSR works because the video card drivers have direct access to the hardware

We're unfortunately limited by the Windows APIs, which don't have a way to clone monitors of different resolutions. If you're not running games/videos, you can use the "Mirror Monitor" function on the Settings > Functions tab. It will clone the monitor to a new window, which you can maximize on the extended monitor. It uses polling though, so it's not good for real-time applications like video or gaming.