I also have a flex tool, and looked several times at how I might mount it.
Short story is..........never figured out how.
The mount for the working end is easy.....but then were the heck do you put the power head without hanging it from the dang ceiling....?
Too much bend in the cable will shorten it's life considerably.
But since I had a regular Dremel too, that is what I mounted, then replaced that with a trim router and never tried mounting a Dremel again......