There was an article on a machinist BB the other day about this and they talked about zapping NiCads with a lot of current to burn the whiskers off. The safe way is with a big capacitor, charged up to about 1.5x the working voltage. Other thoughts were automotive battery chargers or just using jumper cables to a car battery for the 9.2v It was pointed out that if the vent is plugged these things might blow.
I have zapped a NiCad before and it does work but some battery packs have a fuse in them that blows when you do this. (notably the IBM "Convertible" PC battery)
I would suggest putting these batteries in a piece of 4" and don't stand near the ends if you try it.