To get the wire from the cabin into the trunk, you'll more than likely have to pull out the rear seat back and cushion to access the grommets.

The cushion comes out first, push in on the red tabs and lift the front, then pull out. It's pretty light, but watch your fingers, the metal frame is sharp. The seatback is a bit harder, there are a couple-three bolts on the bottom that unscrew, then the seatback lifts up a couple inches and then comes out forward. This one's a pain because it weighs more and it's hard to get leverage when you're hunched over in the cabin. Then you can pull up the insulation and find the wire tracks up to the grommets in the upper part of the firewall.

If you're willing to remove the front seats too, you can use the factory wire channels. If not, you can fit a couple wires under the right and left side door sills, they pop up and the trim along the way can be loosened by undoing the screws.