Autos are easy because there is a hole in the firewall for the clutch cable.
1. Start at the bonnet end, find the unused grommet right under the brake booster, it will come out the other side to the left of the steering wheel down pretty low behind the flip down fuse cover. Then start pulling it through.
2. Remove the plasticy/rubberish lining around the bottom of the door that holds in the carpet and run it under there.
3. When you get to the back seat, you can leave it in (or if you find it easy to take out, go for it. Otherwise leave it). Try to take off the lining up the side of the seat a fair way, you can then go in from the boot and take off the carpet up the side at the back and you should see some light. Stick a big screwdriver or something through the hole, go back to the seat and sticky tape your cable to it, then pull it through.
Its much easier if you've got a mate to help you too!