Complete the game, including the 3 extra missions, to unlock the "Bonus" option at the main menu. From the bonus menu you can see the "Charlie Bucket", "The Wonka Factory", "Wonkabot Troubles", "Violet Beauregarde", "Veruca Salt", "Mike Teavee", "The Special Prize", "Up and Out", "Film Trailer 1", "Film Trailer 2" and "Film Images" scenes.
Find the stairs and with the help of two Oompa-Loompas get Augustus out of the tube. When you will ind several machine, make the Oompa-Loompas work and Augustus will be released.