You're on the same path that many of us have been on, trying to rationalize a solution, and trying to make what the other manufacturers say should work, work. But they often don't work. Often.
So, just to plant a seed, so that it might grow as you're braking up to a light and hear the squeal starting again, on some sunny fall day in the future, I'll post one more time.
Here is what always works - http://www.thezstore.com/page/TZS/PROD/24-5450
Remove the little tab and you can use it on either side. The tab is just a locater, for convenience.during installation. Also, note how the shim only covers about half of the caliper piston. So there's actually a small bending force across the pad during force application. Maybe that's a clue. Who knows.