My take is that early on in TC Bill saw that Petitti was playing better than Fabini or Columbo. So, he is trying the other two at RT to see which one is better at the position. Meanwhile, why not see what Petitti can do at LT? I think he has seen Petitti is doing pretty well there, too, so now he has McQ working over there to see if he has enough to stay in a backup role, or go to the practice squad.
Then again, it could be another Peterman, where he watched Petitti early on, & realized that all the weights in the world aren't going to give Rob quicker feet or hands. So, he has anyone & everyone working OT to try to get SOMEONE over at RT who is better than Petitti. I am hoping it's the first scenario.