Right below the cabin air filter on the passenger side, if you drop down/remove the carpet, you will be able to drill a hole right through the firewall.



(image provided by onigoroshi)

Image 1 (Click image to view in full size)
Drilling where the clutch would be


Image 2 (Click image to view in full size)
The hole from the other (engine) bay side


Image 3 (Click image to view in full size)
Another view from the engine bay side.

In the cabin area, under the drivers side dash area, and to the left of the brake pedal (on the firewall). If you remove the carpet a bit, you will see a perforated area on the foam padding. (a soft plastic-like material that is covering that section). Its a small rectangle with circular corners shaped cover. This is where the clutch would have been if your vehicle was an manual. (If your vehicle is a manual, you will need to use one of the other options listed here.) Drilling in this area might be a bit risky since it leads very close to the vacuum booster. But by measuring carefully, you can determine that by drilling a hole in that area, from the inside, you will not hit anything on the other side of the firewall.

First drill a small hole, to get a wire hanger through and then drill a bigger hole for your wires to get through. Get some rubber grommets at any autoparts store as big as the hole to fit snugly into the hole.

Note: You just have to be certain that when you drill a hole you do not hit the power brake booster or anything else. You can do things like measure horizontally from the steering column or whatever. Remember to measure twice and cut once. Just check and double check and be sure you have it in a good spot, then drill it.

1-Remove the glove box (4-6 screws) see Cabin Air Filter mod for instructions.
2-Open the hood and remove one screw from the weather stripping on the left. (or right side of the vehicle) and pop out all the plastic clips.
3-Lift up the weather stripping and look into it with a flashlight. You will see that filter housing.
4-Tape one of your wires to a coat hanger (that's been straighten) and give the coat hanger about 3 inches before you tape the wire to it.

like this <------------=================
             coat hanger   wire and coat hanger

Fish it through at the top of the filter housing. Either have another person on the other side ready to grab it when it comes out or push it threw and go around and grab it yourself.