How do I FSBO a short sale when I am upside down in the loan?

I owe $350,000 on my house that is now worth about $70,000. My mortgage company will not reduce the principle in order to allow me to get a FHA loan nor will they negotiate. In order for my bank to do a "deed in lieu of foreclosure" I must list my home for 90 days. I've tried to contact a real estate agent to short sell the house but they end the call when they hear how upside down I am in the loan. I understand, it is a fruitless waste of their time. Now I have no choice but to attempt to "For Sale By Owner" just so I can hand over the keys to the bank without owing them the $210,000+ . Is there anyone who has been through this that can lend some advice?