Saw somebody do this on gizmodo a couple weeks ago and decided to give it a shot. I got a can of plasti-dip spray-on electrical tape:
Amazon.com: Plastic Dip Intl. 16003-6 Spray On Electrical Tape: Home Improvement
and applied 3 coats. I am really happy with the result, a nice thin rubberized backing for my pro.
-I did electrical tape vs regular plasti-dip because I wanted a more rubber feel than plastic feel; I'm sure they both work fine.
-Do this outdoors. I did it indoors and the fumes gave me a bit of a headache and are almost definitely toxic.
-Remove the battery backing and place it on top of some sort of level object and then place than on top of a spread-out newspaper as opposed to just putting the cover directly on the newspaper. You want to be able to spray such that you reach the very edges of the cover. If you put it directly on the paper, you'll stick to the newspaper and you won't get nice clean edges. This is important because the plasti-dip, once dried, can be easily peeled off if you want to, so it's important to keep smooth edges that won't snag on something and peel you cover off.
The pictures are with flash, so you see lots of tiny bubbles that look off-putting. In reality, they are subtle looking and add to the nice texture of the backing:
DSC_0337 | Flickr - Photo Sharing!
droid pro plasti-dip cover 2 | Flickr - Photo Sharing!
Also fyi I have the extended battery installed. Thanks for looking.