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"