There's a new mod launcher created by R Lee available for rFactor. It allows you to choose the mod you want to play before lanuching the game and also allows for custom FOV settings. It works great and takes care of the interface problems that some mods create, forcing you to restart the game to get back to the default UI. There's a screenshot below and you can download the mod launcher right here. It's a tiny file weighing in at only 39kb. Be sure to have a look at the included readme.txt before using.