I've been contemplating the same thing. My idea was to make a plate that stretches from the first roof rail mounting point (same place roof racks are mounted), to a second mounting point that's hidden under the widow pillar moulding. Some people have used the widow pillar mounting point to screw down the faulty moulding. I also saw it used on a custom light mount. If it feels flimsy, you may want to join the two sides together in an "H" configuration. You could even hide the plate under all the moulding, and only make stick out a perpendicular tab to mount cable. If you do hide it under moulding, AND have the roof markers, the crossbrace could also be hidden under the roof maker moulding. Does this make sense?
"Ex Umbris Venimus"