Great to see you do this OP.
I did the similar install in my glovebox with the dock cable only coming out of the glovebox(only when needed).
I am going to remove my glovebox soon to put a new USB charger(the old one is being temperamental).
Will post a picture of which fuse location to tap when I remove it.
Will need to buy a new cable now though, thinking of buying iphone 5.