Done this on a Mate's car. You can use the existing grommet on the right-hand side (looking from the front) of the engine compartment. roughly under the Coolant resevoir. You might be able to pop it out, but I had to make a small hole and shove the cable through - Since the rubber had to stretch to allow it through so it still makes a decent seal to stop crap getting through.
After that you should be able to route it behind the glovebox, behind the long plastic trim down the passenger side of the car, and under the carpet where the rear seats are, and voilá! you've got power in the boot.
Assuming this cable has a fuse on it, make sure the fuse is in the engine compartment, or if it blows it might set fire to the interior.
