While playing enter the following:
Load from a point in the game where you have a staff lightsaber, and go to the Main Menu.
Select Quit Game, then select New Game.
Choose your character's appearance and press Accept.
In the lightsaber selection screen you should see the lightsaber hilt pictured is a staff lightsaber, and underneath where the Hilt description should be, there are just left and right arrows. Leave the Hilt as it is and choose a colour then Accept.
You can now start the game from the beginning with a staff lightsaber.