I'm now the proud proprietor of the CAPTCRUNCH photo album, thanks to Mr. Moore. As the photos show or suggest, I started by pulling out whatever I could to gain access to the unknown route from the VP HCU to the back of the E-key. A bit like searching for the Northwest Passage. I tried pushing the cable through the cramped and congested space between the rear of the 12v/110v breaker panel and the outboard end of the rat's nest behind the dash. No luck from either direction...the square-ish plugs on the cable were a real hindrance. Of course, the last thing I tried turned out to be the successful one. By removing the switch panel (wipers, horn, etc.) from the dash, I could actually reach in that opening with my left hand and push the cable end far enough to grab it with my right hand reaching up from the breaker panel opening. In retrospect, I probably didn't need to remove the upholstered armrest. Things remain as shown while we are distracted by the approaching nor'easter forecast to sport 60+ knot gusts.
BTW, I'd like to hear from anybody who has removed the padded trim panel between the head of the starboard V-berth and the helm bulkhead without first cutting it into sections.
All the above pertains to my 2013 R27. Others' results may differ.