But, you can use Racer_S's universal res changer to do it:
Version 1: http://wsgfmedia.com/uploads/paddywak/screenshots/justcause/ureschanger.zip
Version 2: http://dl.tocaedit.com/ureschanger2.zip
1. Download this rar file and un-zip into your Game folder ... where the games .exe is.
2. Open up the <resolution.ini> file and change the resolution to the one you desire ...
3. Start the game it may now run in the chosen resolution.
Side effect: Hor+