Stackin' the yaks'

Does anyone here have any experience transporting two hobie kayaks stacked or nested on top of a cargo rack? Or is side by side the only way to go. I am speaking specifically of either an Outback or Revolution on bottom and a Sport on top - I know the Sport is much shorter, especially than the Revo, but wondering if it could still be secured that way reasonably securely?

I met someone yesterday who nestles his Sport in his Outback.