Al Jefferson would be the most logical choice, based on the fact that he's an all star (if he isn't selected to one this year, that's a whole lot of crap). I don't know how he'd fit on this team though. I guess as a backup big to Perkins and KG who would effectively be the 3rd (and only reserve) big. The only concern would be Al's defense.
Ryan Gomes would certainly be a better fit for this team than Big Baby, and possibly even Powe. I'd trade Scals, Baby, and either Walker or Giddens for Ryan today if I were Danny and McHale were a willing participant. Our bench right now, as it stands, sucks. We need to bolster it with offensive players. I've noticed that when the second unit is in the game, they can actually defend okay, but they can't score. Way too many turnovers, and too much isolation. The only guy who should be calling guys off is Powe. At times Tony can be a threat but he's usually out there.