Maybe a silly question, but why not introduce a fee for placing an order?
Let's say 50% of the current fee which we have to pay to the exchanges. The exchange gets the other 50% when there is a buy/sell.
This way ONLY the real asks and bids will be at the exchanges. No playground for people like Nemesis (if he's the right person), cause he'll lose (a lot of) money to place such an order in the first place...
I think it could be better for the near future of BTC (new money).