This will affect a critical system file for the game. Make a back-up copy of the file before you edit the heck out of it.

Locate the /Program Files/Singles2/Config/ directory and find the Game.* file. Edit that file using a text editor, such as Notepad. Locate the following code and make the following changes to your file:

# min window size
minWindowSize = 320 200
# min/max window aspect ratio
minWindowAspectRatio = 0.56
maxWindowAspectRatio = 3.59
# pixelate (instead of black bars)
pixelate = true