I have been thinking about this also for sometime but I agree it can and would be dangerous for the reasons below.

1. You fall off - boat sails away, maybe/probably.
2. You tether yourself to the boat with a line - you get dragged and potentially drowned in the process.

I am thinking of somehow engineering the tiller so that if its 5 to 10 degrees above the deck, ie held in your hand, it locks some sort of friction mechanism. If you fall off the tiller returns to the deck due to gravity and unlocks or puts your rudders in a slight turn....

Sorry, I'm a design engineer and can't stop the brain...

Now I can't see any simple way of doing this yet but I will tinker away. Any thoughts on this idea???