I did this today and I'm well chuffed with it. Hid the switch and cable in the cubby hole in the dash. I could never get a decent reception with the FM transmitters. Its not that hard to do either
I did this yesterday and it works a treat too. Really easy as I have no experience in this kind of thing and figured if I made a mess of it I would then have the excuse for getting a new head unit. Didnt want to do that though as it would cost a fortune. Next plan for me is to integrate the button on the iphones headphones that will allow me to start/stop/previous track/next track the iphone without having to unlock it everytime!
Thanks to the OP for the how to again