When you run the cables, the shortest route is to run it down under the centre console then carefully take it under the carpet by the gear stick and feed it towards the back of the car until it reaches the end of the carpet which is under the rear seat (which just unclips and comes off), then you can run it under the rear armrest where there is a hole in the metal but it's covered with a rubbery material (kind of sound proofing stuff) that you can puncture. If you feel around at the base of the armrest (when the rear seat is removed) you can feel the hole, you just have to punch through it...this takes you into the boot right in the middle, from there the world is your oyster!!! This does take a bit of time this way, but it minimises the chance that you pick up any noise as other routes can take the cable past the ECU, or alongside power cables...plus as it is the shortest route you have plenty of length to play with in the boot instead of running out a couple of inches short! Typically...
Good luck