First, let's look at what the Indians have done:
The @Indians recall RHPs Trevor Bauer and Carlos Carrasco from Triple-A Columbus; option LHP Nick Hagadone to Columbus.— MLBRosterMoves (@MLBRosterMoves) June 28, 2013
It's important to differentiate between Bauer's and Carrasco's status. Although technically Bauer is the starter for the extra game (because Carrasco is the one in the rotation right now), Carrasco has been identified as the 26th man clubs are allowed to bring for scheduled doubleheaders. Because the Indians could not have brought Carrasco back to pitch today under the normal recall rules (he had been sent down on Monday, and normal rules require a waiting period of 10 days unless there's an injury), the Indians used the 26th man rule to not only bring Carrasco back to start today, but so that he will not re-start the 10-day waiting period when he's sent down after tonight's games. So the Indians can start Carrasco today, send him back back to Columbus, and recall him when his spot in the rotation comes up again. Bauer, on the other hand, is recalled like in any other transaction, and the 10-day waiting will apply to him unless there's an injury.
To make room for Bauer (Carrasco could be added without sending anyone down), the Indians optioned Nick Hagadone to Columbus. Hagadone was chosen mainly because he has an option remaining (the other two in the bullpen with options are Bryan Shaw and Cody Allen, and they aren't going anywhere).
Paul Hoynes is already reporting the roster move the Indians will make between Games 1 and 2:
#Class Indians will activate Matt Langwell between games of DH and send G1 starter Trevor Bauer back to Columbus.— paul hoynes (@hoynsie) June 28, 2013
So the Indians will have a 7-man bullpen for Game 1, and an 8-man bullpen starting with Game 2 and ending when they need to bring Carrasco back to Cleveland.