How about just "walk away" - it will atleast signal your self-respect and confidence (ok if you are truly desperate thats a diff thing). I was asked to share my counter offers - I told them that is unethical so would never share confidential letters from other companies. Seemed to have worked just fine - Ofcourse in this market where each job has a 1000 applications short of being the BDFL of a hot field - almost nothing else is not going to help you negotiate.