If you are using FORZA5 's config for other games,
your G27 will only work in Legacy Mode.
In this mode, the console will only treat your G27 as a general controller,
not a real wheel. You will not get the perfect response in this mode.
As for the buttons, if the default layout is not right for the unlisted games,
please refer to the video below for remapping the buttons.
Most possibly, you will only need to remap several of them.
http://youtu.be/aP_9wE4EWBg (ReaSnow Cross Hair Mapping buttons in game)