Chris Carpenter attempting another comback as starter. But who would he replace in the rotation?

In case you haven't heard by now, Chris Carpenter is attempting to make another comeback from the shoulder issues that have plague him the last two years. 

Initially it was reported that the Cardinals were hoping that Carpenter could join the bullpen at some point this season.  However, recent reports indicate that he is conditioning himself to be a starter.

While its great to see him making a comeback and I wish him all the best, I have a hard time finding a spot for him in a starting rotation that is currently the best in baseball with a 2.38 ERA.  But if the Cardinals do decide to insert Carpenter back into the rotation, who might he replace?

Here are the possibilities:

Jake Westbrook

Despite a 1.62 ERA, Westbrook has been the least dominant starter on the team, with just 4.4 K/9 for the season.  He has also allowed 4.2 BB/9.  His saving grace is that he induces a ton of groundball outs, with a 2.30 GO/AO ratio. 

Westbrook is currently on the DL with an elbow injury, but it is not considered serious.  However, if he has any setbacks, Carpenter could eventually step in for him.

Lance Lynn

Lynn has adjusted well to his new weight.  He has allowed just 33 hits in 50 innings while striking out 54.  It remains to be seen how he holds up over the course of the long season, as the main reason the Cards wanted him to lose the weight was because he struggled in the second half last year. 

If he struggles again during the second half of this year, then I could see Carpenter taking over his rotation spot, with Lynn moving to the bullpen.

Jaime Garcia

Again, there is nothing about the way Garcia is currently pitching that would make one think he should be removed from the starting rotation.  He has a 2.88 ERA and a 38/14 K/BB ratio.  He also has been inducing groundouts at a higher rate than Westbrook, with a 2.86 GO/AO ratio.

However, after a shoulder injury knocked him out during the middle of last year, there are concerns that the shoulder issues could return.  Carpenter would be a logical replacement for him if that should happen.

Prediction

Obviously, there are a lot of "ifs" in the above scenarios, but nothing that currently suggests that any of the above starters should be removed from the rotation.  Even if one of the above scenarios did occur, would the Cardinals take a chance on Carpenter, when his shoulder has not shown the ability to hold up under starting conditions? 

I don't think so.  The more likely scenario is that the Cards will use Carpenter out of the pen, and even then they will treat him with kid gloves (e.g. no back-to-back appearances, no more than one inning at a time).  If a need for a starter arises, John Gast or Michael Wacha would likely get the call.

So, while it would be nice to see Carpenter return as a starter, as he has proven in the past to be a big game pitcher, I just don't see him cracking the current rotation.