No guns blazing, but you did say:
"Nice idea. Absolutely wrong product."
I thought that was a little forceful of a comment considering that these products are made for those exact situations....and...stereo rycote options do exist. But, you are right, it is much more expensive and the OP did ask about umbrellas..so, sorry about hijacking here.
One other thing though, you said this:
"...a very small minority that goes to those lengths around here. In my experiences if the weather was so bad that I needed to do all of what you do then most likely venue has canceled or postponed..."
These are not great lengths or for extreme weather conditions. Actually, I find this technique much easier than using an umbrella and it works perfect for light mists. No extra clamps, no umbrella, small, slick and so on. Good enough for hollywood, good enough for me