Wiring in a cabin heater.. LHD VRS

SO I'm looking to wire in a cabin heater in my car since this winter seems to demand it, and i've already got an engine heater connected (defa one) so all i need do is get a T coupling and hook another cable up and into the cabin, preferably in the right hand seats (passenger seat to Me) legspace, so below the glovebox somewhere, ideally along the sides ..

Anyone aware of any access to there, either through the A-pillar or near the center console? Ff there's any slots there, though I'd really prefer not to have to tear down the entire center panels or the entire dash or some such.