If you have an Nvidia card, I have another suggestion.
Create a custom resolution in your Nvidia settings and run your desktop at that resolution.
For example, say you've got a 1080p monitor. It's 1920x1080. If you want a 4:3 resolution, just take the pixel height and multiply it by 1.333333333333333.
In this case, 1.333333333333333 * 1080 = 1440. 1440x1080 is 4:3 for a 1080p display. If you're running at a different resolution, do the same thing.
When you run at a custom resolution like this, there are no stretching artifacts, because you're using 100% of your monitor's height. Mala should work if you do this. I have no idea if AMD has a similar custom resolution setting.