Now that Hoynes has latched onto the Perez rumor, I feel pretty comfortable talking about it :)
Ben Broussard is going to be the Indians' Opening Day starter at first base unless he's hurt. Ryan Garko, next in line for the job, will probably start in Buffalo to "work on his defense." I have no doubts that Garko probably does need some reps at first base, but that's because he hasn't played there very much. But I still think that even with his defensive deficiencies, whatever they may be, he'll be a better option at first than Broussard.
That being said, the acquisition of Perez will help to patch the position until Garko is deemed ready. If you don't want to commit to an everyday player, the least you can do is to find two players who can do the job:
Ben Broussard vs. RHP (career): .263/.335/.469
Eduardo Perez vs. LHP (career): .263/.368/.501
Perez has played some third and a bit of outfield, but he's really just a first baseman now. The Indians will lose some positional flexibility by committing three roster spots to players who can only play first base (and Hafner probably can't do that), but it's worth it to help the lineup against left-handed pitching.