I thought he could play left-back... but I can't find anything that backs that up. You're correct that the right side is full, but if they decided to toss Zebina (which they apparently want to), he would be an ideal option, as he can definitely play CB as well, like Grygera.
I don't think Balzaretti is an option. If they thought he was, they would have kept him. As well, frankly, as much as we like him, I think he and Mathieu stand out from that group in a negative way... they aren't at the same level as Grosso, Jankulovski, Zambrotta, Pasqual, or Lahm.