Thanks Snowy, just spoke to Brenton from Merridian Motorsports, extremely polite and helpful guy. He just finished an install for a rear parcel shelf on an R35 6 weeks ago as you mentioned.
He is wmailing some pics but sounds like a great option that maintains daily drivability but ensures safe harness fitment.
Apparently the aluminium bracing they utilise in the car joins the rear strut towers and is a damn fine bit of engineering, more than capable of safely supporting a harness bar.