Not quite what I want yet...but getting closer!
The original shots specs were the same:
Canon 50D 50mm 1.8 lens; 1/100 F/18 ISO 100
High Speed mode, Live View mode
Took 30 shots like this:
Used Imagemagick to create this "averaged" composite:
convert -average *.JPG converted.jpg
I also played with Canon's Digital Photography Professional 4 software which can make composites, but what I found is each photo was quickly increasing the exposure. The blades are more or less what I want, but it will be time consuming to do this -- I suspect I have to copy the current raw files, drop their exposures, and possibly make several intermediate files to combine later in order to stop overexposing.
Additionally, even though it's just a couple seconds the clouds moved enough to blur significantly -- his might be a candidate to Photoshop to keep a single background and substitute in just the composite windmill. Hmmm...