Just go to the folder GPSAVES\Carsets\Fsone 2009\Data\F1graphics\1024 x 768\ and edit with notepad the f1graphics.cfg file inside this folder, change the 2nd and 3rd line:
1024 ; [RELEASE] Game 3D Horizontal Resolution
768 ; [RELEASE] Game 3D Vertical Resolution
to look like this:
1366 ; [RELEASE] Game 3D Horizontal Resolution
768 ; [RELEASE] Game 3D Vertical Resolution
Next time you choose in CSM configurables the resolution 1024x768 it will be 1366x768 in game.