It could be done, however it would be a bit of a hassle. One tracking down the schematic, getting the correct parts, and all of your labor to build the darn thing, its just as easy to get the cable from Mitch, especially with the low cost of the units on ebay nowadays.
I just wish it responded faster.
TruckPC - gutted, being used for test setup
BoatPC - All in 1 in cuddy, N7 using VNC on dash, RR
BlazerPC - Nexus 7 with Timur's USBROM
why would you build your own when ur looking at 15-20 in parts and he sells the cable for 26? just seems pointless unless ur trying to learn something. I'd say the price is worth him spending hours getting the interface to work building the software for it and supporting guino in getting it to work in RR.