I'm a big proponent of limiting the amount of appearances the fifth starter makes throughout the season by making more judicious use of off-days. I'd go so far as to advocate that teams building their roster each season should be more concerned with locking in the first four guys in the rotation and allowing for an annual open competition for the fifth starter's role. Then, until the winner of the competition proves that he belongs in the "real" rotation, he can shuttle between a starter and a long reliever role.
Anyway, if they wanted to, the Mets could go without a fifth starter until April 12 while keeping everyone on "full" rest (four days between starts).
4/3: OFF DAY
4/7: OFF DAY
However, if the Mets stay creative, they can instead give a spot start to Jorge Sosa and turn the rotation over for another seven days. Sosa would likely need to be kept out of action after April 8 to prepare for the start, leaving the Mets with a *gasp!* six man bullpen for a few days. Yes. he'd probably limited to 5 innings or 75-85 pitches, whatever comes first. But by spot-starting Sosa, look at the way the rest of the rotation falls in line:
4/14: OFF DAY
This gets us all the way to April 19 against the Phillies, at which point the Mets would need to begin employing another starter to round out the rotation - the next off-day isn't until May 1. Like I said, Sosa could just step into the breach for a couple of weeks, but most teams aren't willing to employ a six-man bullpen for any length of time anymore.
This scenario allows the Mets to avoid calling up a starter and instead allows them the opportunity to add a badly-needed sixth infielder to the roster. Right now, Damion Easley is the backup at four positions - which is more than just a little silly. Recalling Fernando Tatis adds a corner infielder to back up Wright and a platoon partner for Delgado.
Now I am admittedly ignorant of DL rules, so I'm not sure if the Mets would have to keep Tatis on the roster until Pedro returns. However, I believe he could be sent back to New Orleans on April 19 and Figueroa could be recalled to begin making starts in Pedro's spot in the rotation. If not, the Mets could simply option/release Brady Clark to make room for the replacement starter. Keeping Tatis on the roster at the expense of Clark makes perfect sense - right now the Mets are suffering from an unusual alignment of five infielders and six outfielders.
We'll see how it all works out. I do hope the Mets will be creative here and find a way to make this injury work to their advantage.
UPDATE: Creativity is in short supply around Shea Stadium.
From the article: "While manager Willie Randolph didn't say who might start in Martinez's stead, he did say who wouldn't -- Jorge Sosa. A person in the organization had characterized Sosa as the most logical choice Wednesday morning because he is a considerably stronger and more competitive pitcher than Figueroa and because he was ideally placed to take Martinez's spot ...
But Randolph indicated he preferred not to upset the balance in the bullpen personnel by removing Sosa. Now, of the eight pitchers not in the rotation, Figueroa is the most likely to start. But Randolph said he had no person in mind because a need for the starter doesn't arise until April 12."So if you don't need a starter for another ten days, why is Nelson Figueroa here?