Dancing trees and flowers:
During game play press Z + T. 

Listen to radio during credits:
During game play press Esc. Turn on the radio and click on the red brick when prompted to exit. 

Flight Mode:
Enter the elevator in the Information Center. Allow one minute to elapse while in the elevator.
Then, use the cursor keys to fly around the town. 

Play as the Brickster:
Start the hospital mission, but do not save anybody. Wait a few minutes until you are arrested then
you will become The Brickster.