Question: Who is performing in the back stage position for the song "Der Kapitan"? Show the first name and last name.
SQL: SELECT T2.firstname, T2.lastname FROM Performance AS T1 JOIN Band AS T2 ON T1.bandmate = T2.id JOIN Songs AS T3 ON T3.SongId = T1.SongId WHERE T3.Title = "Der Kapitan" AND T1.StagePosition = "back"