yes you can, you need to get one of thoses school magnets positive one side negative other side,
you need to place on the inside of the cover, be careful as a technician can tell if your not that its been tampered with, it goes vertically in the left of the spinning thing and depending on the size of the magnet it will slow it down by X%
obviously do not condone doing this and you should pay for electricity like everyone else does
it is a criminal offence punishable by heavy fines and even jail to defraud the electrical company if you get caught