You could make yourself a cradle to suit.I guess you made the boat.It should be a quick fit on and take off of the bars,just nesting there with some fore and aft restraints.Attatch the ropes permenantly to the ,low profile ,cradle then making sure they run under the bars and over the boat and inside the bar to roof mounts so the whole lot doesn't slide to the sides.I use,what I call a "Truckie knot" to tie them off.Make a loop in the rope before threading the rope tail around the bar then back through the loop to tension and slip knot to the loop.Very quick and also has some idiot proofing,if you design it that way.Make the cradle out of wood!
I see hundreds of cars with these hull horns on the roof bars, whistling in the wind, when rarely is a kayak sitting on them.The "horns" must be fixed on the bars or is it a status thing?"I've got a kayak,somewhere" Yeh,right!..Criminal design philosophy,imho.And the rusty horns cost a fortune.
Cheers from Paul.