Question: What is the first and last name of the artist who performed back stage for the song "Der Kapitan"?
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"