[impassebreaker]

Actually built something that sort of deals with this. it's at www.impassebreaker.com. IB compares bottom line financial positions and if there's a match, you're both told what the number is. A match is any case where what you are willing to accept is greater than or equal to what they are willing to pay. If no match, they don't learn your bottom line and you don't learn theirs. It was built initially for dispute resolution but salary negotiation works fine.