Routing power cable from battery

I have a radio transceiver fitted in my Superb Mk2 estate. At the moment it is sitting on a rack on the passenger seat and run from the cigarette lighter on the centre console. I am now looking at fitting a larger unit which will need about 25A and will be mounted in the box under the passenger seat with the headset on a dash mount. In my previous car (Mondeo) it was easy to route a cable from the battery through the firewall alongside the main loom but looking in the engine compartment there does not appear to be a similar route in the Superb. Has anybody done something similar and can advise on routing?