I use a yoke we made specially for the Poke boats we paddle.  It is a 3/4 inch clear board with a curve cut out of it for one's neck; and it is long enough to just cross both side combings at the balance point.  I use a 4" metal wood wowrker's clothespin-like clamp on each end, I can JUST get it to span the end of the board and hook onto the combing; on each end of the yoke.  Yoke is padded with an inch of closed cell foam and that is covered over with some cordura which is tacked all around (like upholstery).  Since my yak is just 28 pounds it works for me; something heavier might not be able to rely on the clamps. 
I have broken the board in the past, but it is easy to make another one back at home.  Without a yoke I can still portage with the yak resting on my head and both forearms to support it.  It is fine for short portages but gets tiresome on longer ones.
With the yoke I can carry a portage pack and the kayak.  The yak rests nicely on the top of my pack behind my head.