I used to use a penalty box system. Basically, dice that had committed an offence (poor rolling) were assessed a penalty and placed in a sealed tin. The length of thepenalty was comensurate with the damage their poor rolling inflicted--if it was an important saving throw, for example, they could expect to be out for most if not all of the rest of the session, whereas a failed balance check would result in a vocal reprimand and a short stint in the hole.
I used this system for about 2 years, but the anticipated results (higher rolling average--I was hitting much less than statistical average since my dice were evil) never came. I have since abandoned my old system and have now adopted a much harsher penalty. I haven't even considered using those old dice in the current campaign (which is about 3 months old).
Maybe neglect will bring them around. I don't know what to do anymore. I mean, I know they're evil and cursed, but they are MY evil and cursed dice, ya know?
I still have my firts set of polyhedral dice (transluscent light blue with a transluscent orange extra d10) minus the stolen d4. They have history. Granted, it's a foul history, but it's my gaming history.
I'm pretty sure they were cursed when some fool touched them. It should be a mortal offence to touch another gamer's dice. Maybe next time someone touches my dice, they should spend some time in the penalty box.