there is one that you can use in the passenger side, not exactly in the firwall, but in that part of the structure i guess, and the wire will feed in behind the gaurd panel, and then you have to feed it into the cabin using another hole that is already there in the door jam. then you unscrew the scuff plates & poke the wire down under the carpet.
your other choice, which is better for less alternator noise thru your speakers, is to attach a consuit to the underside of the car, feed the wire thru that, and then feed the wire into the boot from say, for example, the spare tyre well, ir you use that option, its best to drill a new hole and fit it with a suitable rubber grommet so that the wire passes thr a water tight hole.
i believe that its also possible to run up to 8 gauge wire within the trx side skirts, but they're a bitch to get off.