Hi Chris.

AFAIK, you don't need a cable to update the firmware. It can be done over bluetooth. Getting the VW firmware will probably be difficult though.
The VW touch phone kit is actually a rebranded Bury CC9060 (I think). So you might be able to reflash the control unit with the Bury firmware which I think can be downloaded from the Bury website.

Sorry, but I've never had to update one of these phone kits so I can't really offer much help. I did do a quick google search though and found this...
http://www.bury.com/consumer/fileadm...oftware_EN.pdf

Good Luck!