I used the command-line utility xrandr to fix the problem. Running the tool with no arguments prints a list of displays and available display modes for each. This is handy since you need the name assigned to your display by your OS for the next step. Next, use the “–newmode” option with xrandr and specify the modeline which describes the display configuration you wish to use. This modeline generator might help you create the modeline you need. Once you create the new mode, use the “–addmode” option to add it to the list of modes supported by your monitor.

Finally, add this command to your ~/.xprofile file (or something similar) so that when you start your machine the new mode is automatically added and available (this way Ubuntu automatically reselects it too). This is what I ended up adding to my ~/.xprofile file:

xrandr --newmode "1920x1200_50Hz" 128,300 1920 1968 2000 2079 1200 1203 1209 1234 +hsync -vsync
xrandr --addmode HDMI-0 "1920x1200_50Hz"

Note: If you set your refresh rate too high, your monitor will probably flicker occasionally. If this happens, try lowering the refresh rate by lowering the pixel clock value (the first number in the modeline).