Hey David!
I was kind of wondering about a single point of friction myself.
Didn't think about the pressure breaking the wire but I can see that as a possibility at some point. Also the set screw threads might be a bit weak in aluminum. Crap! Back to the drawing board.....
So another thought.... I'll redraw it and you guys can check it out. I like visual stimuli my self!
Imagine if you will the same cap screw and aluminum rod. However, now the end of the rod is still drill for the wire to go through and the hole is still in the top but with no threads. That is where the end of the guitar wire will drop in. (the part with the stop) Still very clean, no pressure on a wire, and no chance of slippage. The other end will be inserted through a hole in a machine screw and then wrapped around a couple times. The screw will be held in place with a jam nut.