How to get a 4awg power wire through the firewall!

Hi all.

I'm midway through a project involving installing aftermarket amp in the boot of my Fabia Mk3 (1.0 TSI, RHD). However I can't for the life of me find a suitable, accessible grommet to route my 4 gauge power cable from the battery to the interior.

I've removed the glovebox and kick panel, but still can't find a grommet. I've tried the one underneath the scuttle panel on the passenger side, but the seal is way too tight to accommodate an additional cable.

If anyone has successfully routed such a cable on their RHD Fabia, let me know what grommet you used and if anything needed to be removed to gain access!

Any advice would be really massively appreciated
Cheers