CHAdeMO communicates over the CAN protocol and requires a certain handshake (per the CHAdeMO spec). You essentially need a few parts, contactors, HV wires, CHAdeMO port, 2 channel CAN controller.
A good place to add the contactor box is by the inverters as these have a direct link to the battery and the location is a relatively cool place in the car (don't need some fancy IP67 rated enclosure etc).
Our solution, at least what we are doing to our cars is using the Model S chargeport which can utilize a CHAdeMO adapter. This way we don't have to package an additional CHAdeMO chargeport on the vehicle itself. There is really no clean way to put this on the car and most don't want to drill into the body panels of the vehicle. I am doing something similar to my Tesla Roadster as well.
We don't really use hobbyist grade "hacking" tools but essentially auto grade components that meet vibration, temperature etc specs that are equal to or greater than what is in the vehicle currently. I am not sure how long a raspberry pi will last in an auto environment (no conformal coating, vibration spec of the solder joints, temp specs etc). Liken this to putting your iPhone or some device in direct sunlight during a hot day for a few hours. It will likely shut down and be unusable. This cannot happen when driving your vehicle. The hobbyist grade stuff likely will not hold up in this type of environment.