I'm just thinking what exact setting it was that helped with that issue. I can't really remember but I used some pretty "standard" resolution (in OpenGL) and something in card settings that helped solve it. As far as I remember I simply experimented with various graphic card settings and it helped.i'm playing in 1920x1080 and everything is stretched . . .
Anyway it should make it unstretched, in the middle of screen with black stripes on sides filling unused space - it's still much better than stretched 33% to the sides.