Why do you need 12ga. speaker wire for your door speakers?? That is huge, it's what I used for my sub in my old car.

Anyway, if there is any room in the factory rubber boot in the door jamb, you can just pop it out of the hole in the body and the door to get the wires through. This is how I ran the wires for power door locks that I installed in my old car. You're asking about drilling a new hole? I would suggest trying this method first if you haven't already.