Why Mientkiewicz? Why now?

There's one aspect of the Mientkiewicz (which I've finally learned to spell) signing that I don't get: why the hell would he sign a minor league deal with the Pirates? He's left-handed, he's a league average hitter, and even if his defense has declined in the past couple years, he's got a reputation as a Gold Glover that many people refuse to look past when evaluating his play in the field. How can a minor league deal with the Pirates be the best he can do? The simple answer is that it probably isn't the best he can do and that the Pirates offered him something that he couldn't get somewhere else: playing time. The only thing that makes sense here is that this move portends a trade of Adam LaRoche or maybe Xavier Nady. It's not that the Pirates can't find room for him on the roster because they can- no one's forcing them to bring in another backup catcher and Huntington's already said he's got no problem with Pearce starting in AAA. Knowing that Russell was a no-hit backup catcher for a lot of his career, I would think he wants a guy in his mold to back Paulino up and won't accept Doumit's bad defense and gimpy hammies (though he doesn't get the final say). That means that between Doumit, Nady, and Pearce, Mientkiewicz is really redundant. The only way this move makes even a modicum of sense for either side is if LaRoche or Nady are traded, and soon.