Here's a thought...use a couple of those harken micro-through hull sheaves running part of the line internal to the rudder arm...The black standoff on top of the arm could be adjustable to control the angle of the line leading to the flip lever allowing you to really dial in the amount of pressure required to automatically release the rudder from a ground impact (or fish).
Like your idea as well. Please keep in mind that the intention is to both lower and raise with the one arm [see the second line on the picture-lower on the arm-other side]and and it can be converted back to the original system without any damage [as safety when making this system up]. When sailing on to the beach I normaly release the arm from the black "clamp" [not sure if this is correct English]and pull forward to raise the rudder.
The "pull forward" is not realy needed, the rudder will be raised gently by the beach.
If the rudder is in lowered position it "sticks" there due to the fact that the arm is over it's turning point [line attachment is slightly lower then rotation point - bottom of arm] The attachment point of the both lines are very importent!! this took the most experimenting to figure this out.
If something hits the rudder when in lower position and in clamp, the rudder will come up if the resistance of the both the clamp and the "dead point" is overcome.
At the beach I keep the rudders "up" with a little bungee "o-ring" that is near the tie-rod
It is a bit of long description but I hope it is somewhat clear.