Copy the "CFS3.exe" from the CSF3 install into the OFF game folder - delete the old "shell.exe" there first, or backup the file with a different name (e.g. Oldshell.exe). Then rename the copied "CFS3.exe" in the OFF folder to "shell.exe".
I'm sure thats the way i got it to work
http://forum.combatace.com/setup-phase-only-t37679.html