I've heard there is a "machete hack" you can try in your PC's registry, but I can't say for certain that it works or if it makes your game unstable:
Under "HKEY_CURRENT_USER\Software\UBISOFT\Far Cry 2" the entries "PartnerKey1" and/or "PartnerKey2" get set to 1 [DWORD]. (Btw, add the entry...