If you turned into a dog, you wouldn't have to find a bathroom. Of course, it could be awkward if you turn back suddenly after you're done... then you'd be a guy with his pants down who just pooped on the grass.

eat a bunch of chili and drink lots of water, ~30 mins later rob jewelry store. Before making an exit make sure you start to feel it. Stash in safe location, and hold it in.
perfect disguise.