At the title screen select "Password" and you will go to a screen where you can enter a 4 character password. You can select from the following symbols: Rock (R), Paper (P), Scissors (S) or a Blank Space (B) to start at the desired stage.

Effect	Password
Start on Floor 6	P-R-P-S
Start on Floor 11	R-B-S-P
Start on Floor 16	P-S-S-B
Start on Floor 21	R-B-R-P