I am going to have a go at answering Trevs question. I have not heard of any sort of device that will stop your kontiki drifting away when the line has been cut .
It all depends on were the line has been cut so let's say its been cut on the stoppered section as long as you have a weight fixed at the kontiki end you should be ok , it may drift but it should give you time to organise a rescue .
These new auto pilot jobs may be a different story as they don't like a heavy weight .
Hope this helps .