Raspberry PI car OBD2 computer

Looks very cool! I coincidentally spent most of the weekend reading about OBD-II and CANs. I'd like to get a RasPi/Arduino with a temperature sensor connected and send CAN messages to regulate interior temperature for example.

From what I gather, CAN messages are not broadcasted through the OBD port for sniffing, but once we know the proprietary CAN commands (VW in my case), we can send them through? Ie. For finding what car button sends what message, does one have to splice some cables to tap into the CAN bus? Dr. Charlie Miller & Chris Valasek wrote a nice paper on the subject back in 2013, and they hacked together their own cable: http://illmatics.com/car_hacking.pdf

Being able to control the car's to implement my own features from reverse camera to remote start sounds very appealing.