Hyperspin on ultrawide monitor; any way to force aspect ratio in fullscreen?

[Landcross]

I'm new to Hyperspin and I've run into a little problem. I have an 'ultrawide' monitor with an aspect ratio of 21:9 and a resolution of 3440x1440. I can understand Hyperspin does not natively support that resolution, but is there any way to force it to run 16:9 (with black bars). Because when I start Hyperspin in fullscreen mode, it's stretching 16:9 output to 21:9 which looks horrible.

I've tried fiddling with the Nvidia settings to properly scale the image which worked before on another application (can't remember which one), but it looks like Hyperspin actually stretches its own image to fit the 21:9 aspect ratio before its rendered on the gpu or something because even with gpu scaling on in the nvidia settings it's still running a stretched 16:9 image instead of actual 16:9 with black bars.

Any help, tips or tricks to get this running fine?