I'd like to know this as well. I've got an '08 GTI with a CarPC also.
From what I've found, you could probably just use the SWI-CAN to convert the can-bus signals into an anolog signal (voltage/resistance), then use the Fusion Brain interfaced with the SWI-CAN to control the PC.
Only thing is, I'm not sure what the SWI-CAN outputs. If it's still just outputting a can-bus data stream, then obviously it won't work.
Can anyone confrim exactly what the SWI-CAN outputs and does?