Well, I just ordered parts from China to make this work without breaking any factory wires. Only catch.. my WRX doesn't come till July, and the parts from china will take a month anyway.
I cant say for sure this will work, but if it does I can make them and sell them for ~$5 each to people.. I had to order enough to make 20 to meet minimum requirements. They will cost $3.50 in parts each and require about 5-10 minutes each to put together... and will probably be wrapped in electrical tape so it wont look professional. But it will be as easy as plugging in connectors for USB and the 4 pin piece factory harness.
Im not comfortable sharing what I bought as I cant say for sure it works and dont want to send people off.. it will require some soldering to make the 2 parts work together and some testing to get the right pin outs anyway... If I get it working Ill post a tutorial with LOTs of pics and video because i know there is a high demand for this function.
However, since I dont have my WRX yet.. Im wondering if someone can share with us (if it is possible to see) which color wire goes to which pin hole on the 4 pin connector? If it isnt visible, and someone out there has already cut theirs it would be great if they could use a multimeter or conductivity tester to see which color wire goes to which hole. <--- or maybe someone will volunteer for the community!!