You could try taking them out and smearing some copper or ceramic grease on the backs. Gently sand the friction surfaces on something flat, just to get rid of the glazing. Usually does the trick at work.
WHIPE THE DISCS WITH SOME ALCHOL TO REMOVE ANY GREASE OR SOAP FROM BIKE WASHING LIQUID USUALLY HELPS(OOPS )JUST NOTICED I AMSHOUTING TOO LAZY TO RETYPE!