Making the plate is the best way...If you don't mind a little work I would run new wire into the door for the crossover. You can do it drilling any holes in the metal of the car...just take your time. The passenger side is easier than the driver side, at least, in my car it was.
I don't have a how to but I do have some pics, but no way to post them. If you want to shoot me an email I'll send you a couple of the doors and the spot where I ran the wire.
brantleyiii@earthlink.net 
