Normally you'd run it through the clutch grommet but since its a manual you wont be able to do that. next best thing i can think of would be to run the 0 gauge under the car cable tied on top of the fuel rails (not below) and pushing it up either through the rear passenger foot well (there will be a draining grommet used to drain the footwell incase of flooding) or through the grommet in the spare wheel arch.
Either that, or on the passenger side at the firewall, pretty sure there is a section of the firewall that isnt metal that you can drill a hole through into the front passenger footwell (behind glove box) Its like an insulating plastic / foam and you can spade bit through it.
Dont go to the passenger side. You need to keep the run as short as possible and that would stack too much extra length on it. There are main wiring grommets on the drivers side you can use. Just make a nick in the rubber, lube up the cable and feed it through. If in doubt... drill it.
I don't know about too much extra length.. Once you've run from the battery to the firewall, to go from the drivers to the passenger side in the engine bay is <1m. Normally when you run from battery you go from the battery, up to the firewall, towards the motor (right side of the brake booster) then inside the cabin, then back across the steering column into the door sills which in itself is almost a meter anyway