If someone can post some clear, close-up pictures of connector "i26" (the 15 pin connector that you're adding the aux wires to), I may be able to get the correct pins to snap into the plug. Perhaps even the shells to make a plug-and-play insert harness. Either way, much cleaner than the "shove wires into the holes" method
I need to see the pins side of both plug and socket. The top, bottom, and either left or right side of the car's harness plug would also be helpful.