In the three weeks that remain before rosters can be expanded, the Twins are pretty certain to make some moves. First, Trevor Plouffe will be activated from his rehab in Rochester which will force someone to be sent down. The people's choice for demotion would be Nishioka, but it isn't a sure thing that the move will be made. There is a chance that the Twins will go down to 12 pitchers and add another bench player. That could mean that a pitcher on the current staff, such as Manship or Perdomo could be sent down and Nishi would stay.
Meanwhile, two or three pitchers are knocking on the door. Pavano has pitched a rehab start and Walters has made two rehab starts at Rochester. Both seem to be at least a week away. Of course, the Slama issue will need to be resolved. His numbers at Rochester are fantastic and he is not on the 40-man roster. The Twins will almost be required to promote Slama at some point this season. It is my understanding that Slama would be a free agent if not added to the 40-man. The Twins have waited this long, so it wouldn't surprise me if they didn't promote Slama until after rosters can be expanded.
If the Twins decide to demote Nishioka and add a bench player, there are a couple candidates for promotion. New acquisition Eduardo Escobar will probably at least be promoted when the rosters expand, if not before, and Pedro Florimon was the Twins representative in the AAA All-Star game (Florimon is not on the 40-man). The Twins will have to make several 40-man adjustments as well. If they promote Florimon and/or Slama they must be added and if Walters or Pavano are activated, spots must be made for them.
Candidates for demotion from the 40-man roster would include Nishioka, if they decide to send him down, Perdomo, Kyle Waldrop, basically a soft-tossing middle reliever, and perhaps Rene Tosoni. Also currently disabled Anthony Swarzak and Matt Capps could be sent to the the 60-day DL. Of course, when the season is over, the Twins will have to add several minor leaguers, while losing a few free agents. It is interesting and will continue to be interesting what moves the Twins will make.