if you open the passenger door you will see a bit of black foam near the top of the gap between the inner and outer wing. removing the black foam will allow you to route the wire from the battery through the gap where the foam was and then down to the round rubber blank inbetween the door hinges. making a small hole in this blank will allow you to force the wire through it, then push it down a good few inches, it will then be in the footwell with a bit of fiddling. i found long nose pliers helped me grab the wire and pull it into the footwell. you need to move the black rubber thing with wires going thorugh it to one side to be able to see the new wire behind it. once done you can replace the black foam. the only evidence that the wire is there will be the few visible inches of wire from the black foam to the round rubber seal in the gap between door and wing, i used black wire so it isn't noticable at all. from the footwell im sure you can figure out how to route it into the boot under all the plastic trim.
i only used this method because i couldnt find the rubber gromit in the bulkhead, but it is there somewhere if you can find it and it would be an easier method.
