I haven't tried the product you mentioned but I may experiment with some high gloss Krylon spray I've used for some wood jewelry I've made. It would probably still allow me to flex it a little if I needed to tweak it. I would do it after putting the wire through and shaping it, spray (or try your product) and then attach the beads and the top and add another half sole that's been enhanced to hide the taping or gluing of the top to the sole.
My only concern with the product you mention is if it doesn't allow any flexing you'll need to make sure the shape of the sole is where you want it before treating it...will be anxious to see what you do!
Post it here and/or on my blog, (if you like).