I just bought a dock, andan MHL adapter off ebay. I already have an alarm clock with a micro-usb dock by my bed for charging, so I was going to use these to make a multimedia dock for my TV. You can power the MHL adapter so that it draws less power from the phone, but as far as I know it can't actually charge the phone.
Since my account is new, I can't post links, here are the item IDs for the ebay items:
MHL adapter: 161009409501