Well, if Zim is really and truly healthy, you could think of playing him occasionally in left against a lefty if you are committed to playing Bell.
It's very hard to map out 350+ PAs for Zimmerman. I took the # of LHP pitchers with > or = 10 IP, ordered them by # games, eliminated those with over 6 appearances (the number by Kershaw), and guesstimate that there are about 45 LHP in rotations or as the long guys after openers. That's a bit less than 1/3 of of starting slots (150). Figure that amounts to about 54 games vs. LH starters or long guys, and maybe another 6 in AL parks (2/3 of 9 more b/c he'd already be facing AL lefty starters). That's roughly 60 starts, assuming Bell never starts against a lefty. Give him 60 starts, and that's about 250 PAs. Even if he PHs and stays in games, I don't see an easy path to more than 320 PAs.
