1) He'd make a very nice LF... does your current LF have a better arm?
2) The number of (-) plays lefty 2Bs make is not as high as it should be, and while I think you lose some DPs it may not be huge. I played this gentleman at CF, but another owner played him at 2B. Check out the stats-- with a range in the high 70s, glove of 89,and arm ratings in the 60s, he was on pace to make "only" about 25 (-) plays in a full season, with 85 or so DPs.
And it's even less of a penalty at 3B; check out this "left-handed SS" type, only about 12 (-) plays per 160 games at 3B (although with those ratings he'd have a bunch of (+) if he were right handed).
Long story short, I think if you've got a guy whose bat will support giving up 20-30 or so extra runs you can get away with this. I'd try not to, though; usually you'll get better results by changing positions around with your other players.
EDIT-- to be excrutiatingly clear, I view the lack of an adequate penalty as a bug and would love it if as part of an update the penalty for a playing LH infielder were increased.
10/13/2010 4:51 PM (edited)