Where the 1/4" braid line enters the rudder blade, you'll see a plastic cap on the side of the blade about an inch in from the edge. Just pop that cap and you'll be able to feed the line into the hole and put a stopper knot inside like a figure eight knot. The rudder pendant line should also have a 3/16" X 12" bungee attached to it with a "Hog Ring." I have a sketch of it if you don't have this on your rudder. It adds tension to the rope when the blade is up and supposedly keeps the line from jamming between the blade and the aluminum rudder head.
I wouldn't say that you are over concerned. The line is flimsy for a reason. If your rudder blade grounds out in shallow water, something is going to give and usually the line tightens up and you can almost hear it as it tries to pull out of the self rescue clam cleat under your tiller. My tiller split in half one day during a race. It was a laminated type tiller and one of my friends was steering the boat at the time. I would have rather had the rope break, but it didn't. What is really needed is an automatic release clam cleat on the tiller and they do have them. http://www.apsltd.com/c-1022-clamcleats-v-cleats.aspx
In the book "Singlehanded Sailing" they show how a swivel cam cleat can also be made. It works on the same idea but a cam cleat is used on a block of wood held on by a bolt and wing nut. You would need to use your imagination to make it work on a tiller and it would be a little too bulky. I don't think that their automatic release clam cleat would work on the tiller upside down. So it's back to the drawing board I guess. To tell you the truth, when I'm out in deep water, I take about two raps of that 1/4" line right around my tiller after I set it in that cleat, and lay a half single half hitch around the metal peg on top of the tiller which is used for my Autopilot. The reason I do this is because I don't want my rudder creeping up while the boat is sailing under the autopilot. It can put a lot of weather helm in the tiller and cause the rudder blade to flex. If I hit something I try to release it quick. I haven't had any problems lately as long as I'm steering. I can usually act pretty quick. It would be nice to have a quick release cleat for that rudder pendant line though.
At any rate, if you ever hit something with your rudder, you don't want it to break it and you don't want your tiller splitting in two.