The versions of kaitenage I am most familiar with actually throw across uke's shoulders (I believe this is the horizontal componant that Jun refered to). This means that for me (as well as Jun apparently) a jumping breakfall is out of the question. I tend to make a line between the arm controlled by nage/shite and my 'forward' arm, and actually roll across my shoulders along that line; from the tip of my little finger on the forward arm, across the shoulders, and down the other arm (sometimes slapping, sometimes not).
There should be a preferred method in your dojo that is appropriate to the way the throw is used there. Your instructor should be best able to help you there.