I've got a guy in my group wanting to use the Penumbra cantrip for the source of a shadows. I'm not sure if that falls under using your own shadow or not.
I don't think it's using your own shadow, but I would say that it isn't quite enough shadow to pull off shadowdancer abilities. Sorta like standing under a parasol on a sunny day; you're not in direct sunlight, but it's far from "shadowy."