Iíll have to post some pix.
I donít have a kayak, but I do have a Porta-Bote. http://www.porta-bote.com/
It's very much the same idea when it's folded down like a surfboard.
I mounted a Harbor freight Tools board roller on the back of the roof rack. It's made for holding your long boards/planks when using a radial arm saw and the like. I used the base piece for other things, and used just the roller piece itself on the rack. It was less than $20. Here it is:
The roller itself removes from the bracket by pushing a button on one end. I made up a piece of 2x4 wrapped in carpet with holes underneath that match the roller bracket when the roller's removed.
The Porta-Bote hull weighs 70 lbs. When I fold it up, I rest the bow end on the installed roller, and shove it up onto the rack, which is uber-easy with the roller. When it's up in place, I hold up the boat hull with a shoulder, remove the roller, and drop on the carpeted 2x4 and drop the hull back down onto it. I then use ratchet straps to hold the boat into place, and it's road ready.
In my case, the bote's seats and transom go onto the rack under the hull, and for a kayak, you could do the same with your gear.
Unloading's the opposite... switch back to the roller, and the boat glides off the roof rack. I made the carpet-block piece because the ratchet straps make it hold tightly to the carpet. The roller might let the hull slide fore and aft, a bad idea when on the freeway.