I had proposed that Doc make per user CDF available on the Bitminer site. I don't think this is the whole answer, but I think it would be a start to building a systematic approach to the block withholding threat. The good doctor can explain why he didn't like the idea if he's so inclined.
So, anyone who experiences negative variance will be accused of being
witches block withholders? I see that working well. Given recent history, about 8% of the pool would be so accused. If you keep kicking off the lowest performing 8% of the pool it wont be long until you have just one miner left.