You can map the keyboard shortcuts to a switch on your transmitter using:
http://www.lgdb.org/tool/antimicro (Linux)
http://joytokey.net/en/ (Windows)
Regarding the second question - I would be hesitant to add a function to turn off the internal calibration in Freerider since it would mainly just risk causing trouble to 99,5% of the users.
However you might be able to create a script that will reset them (or set them to a specific value). I believe the calibration values can be found somewhere under /home/your user/.config/unity3d