There is a factory hole in the firewall right under the brake booster. Then your power cable is on the same side as your battery and you can run the wire under the driver's door foot guard. I believe that is where PsuedoRealityX (Jess) put his at.

 

(us model)on passenger side on firewall about mid way up is little l shaped tube facing downward. this is the air condition vent tube for the water. there is a simple rubber grommet you can move a little and run the wire through there. just make sure the tube is still connected so water don't leak into your car. i ran a 4 gauge wire through there and it works fine.