Get a can of carb cleaner and place the small red straw just under the left grip and work it around. After a few squirts and some elbow grease the left grip will come off and not be destroyed.
The right grip is a whole 'nother story. I'm not sure if this is the case on '02's, but with my '07 Nightster I had to do the following:
This grip does not typically remove from the throttle assembly. You must disassemble the right grip, making sure that you do not drop the very small brass collett into the depths of the motor where you will never see it again, then simply replace the grip in the reverse order that you took everything apart.
Good luck.
Jake