Sounds to me like you're only option is to sell the property for what you can sell it for, and make up the difference with your lender, out of your own cash.
Also, please make sure to consult with an attorney OR a good tax accountant. The one thing you will need their advice on is making 100% sure that the lender is giving you credit for a complete payoff. I have heard (but have not yet confirmed) that some lenders are now reporting payoffs as foreclosures, when they are not foreclosures.
All the best,