Here's the bench so far. I assume, for the purposes of my argument here, that Ryan Doumit and Chris Gomez are de facto starters at catcher and shortstop, respectively. Feel free to take issue with that assumption in the comments if you'd like to propose some other alignment. Gomez has been the best hitter of the three-headed shortstop monster, and his defense at short, while bad, hasn't been worse than Bixler's and it certainly hasn't been worse than Rivas'.
Obviously, this is a sad bunch. In addition to hitting poorly, all of these guys except Mientkiewicz have had big problems with other aspects of their games as well. (None of the other four play good defense, and the two who have foot speed haven't figured out how to use their brains to transform that speed into baserunning ability.) The bench hasn't been the Pirates' worst problem, but it isn't as if any of these guys are future franchise players, so there's really no reason for the Pirates to stand pat with them.
Just for fun, and taking big trades out of the equation, here's what I propose:
-P- There has to be a backup catcher, and Paulino isn't that bad as far as those types go, so he stays.
-P- Two utility infielders aren't necessary, especially since Mientkiewicz can play third. Option Bixler back to Indianapolis, where he can get some at bats. Keep Rivas for now, but only because (I think) he'd have to be DFAed to go back to AAA. If the Pirates lose him now, they risk running really low on infield options until Jack Wilson returns. So keep Rivas on the bench -- just don't play him -- and DFA him when Wilson returns.
-P- Keep Mientkiewicz, but keep your eyes open for something better.
-P- As per my post earlier today, option Morgan to Indianapolis and bring up Kevin Thompson, who's tearing it up at AAA and could be a nifty right-handed pinch-hitting option.
-P- Get someone cheap who can hit even a little, preferably an outfielder, to occupy the last bench spot. I don't know who that would be, but it shouldn't be hard to find a player who can put up a .700 OPS off the bench. Dan Johnson was DFAed by the Rays last week. The A's recently signed Joe Gaetti. A defensively-challenged guy who can hit even a little would be an improvement. Craig Wilson might fit the bill, but first he needs to hit better at Indianapolis.