Another possible approach is to drill a hole in the top aft corner of the rudder and fit an eye bolt through it with eye nut that attaches to the other side (not sure of the proper name for this but I think you know what I mean). The remove this setup and fill the hole with something not very permanent - perhaps a piece of dowel or something like that. In the rare chance you need it, you can knock out the dowel and mount your eyes without having to drag them around all the time.
I am trying to picture the situation where you might need this. If a steering cable goes your emergency tiller would do the trick. Similarly for any situation where the head of the shaft is still connected to the rudder. The shaft itself is highly unlikely to break (assuming any reasonable engineering). Perhaps if the shaft could break away from the steel webs inside the rudder (more likely) and the rudder turns independently from the shaft.
We had a steering cable go between French Polynesia and the Cook Islands this year and I was able to rig a new one (spares are a very good thing) in something like 6-8 hours. Had to be very careful as the rudder quadrant was moving in the waves and the chance of crushing a finger was pretty high. Annoyingly enough I had inspected the cables about 6 weeks before and they seemed fine. Ainia is a centercockpit and the steering cables are long and convoluted. The breakage happened in area where there was no inspection port and I only had been able to check at a distance with a flashlight.
Finished the circumnavigation in early February in Grenada. Have to work on a book project for the next several months so the boat will be waiting for next year.