What do we do now?

What is the name of your state? Wisconsin
My fiance, while still married to his ex-spouse, co-signed on her car loan. During the divorce, financial disclosure papers were filled out stating that the loan was no longer in his name (the forms were completed by his ex-spouse) He was told that his name was off the loan and he subsequently signed off on the title to the car thinking he no longer had any interest or obligation in the vehicle. Now, 2 and a half years later, via his credit report we find that his name is indeed still on the loan. His ex-spouse was denied refinancing based on her debt ratio, as well as the fact that the amount owed on the car is more than it is worth. The loan on the vehicle will not be satisfied until 2005 and the bank says they will not refinance her with a different co-signer. What can we now do? Can we sue her in court for giving false information on the divorce papers? Can we get a court to order his name back on the title and sell the car? Can she be forced to sell the car? We need some advice here as to what to do next. We are trying to get financing for a home purchase and are unable to do so with this loan on his credit. Had he known that the divorce papers submitted to the court were false and that he was still responsible for this debt, he never would not have signed the divorce papers or signed off on the title to the vehicle. This was a no fault, do it yourself divorce. She knew his name was on the loan all along and thought nothing of lying about it. Unfortunately, my fiance' assumed that given this was a legal document, that all information provided by her was true. Do we have any legal grounds to sue her for what she has done? Doesn't the paragraph at the end of the divorce papers where she signed her name stating that under penalty of perjury she claims all information provided to be true and accurate, have any weight with the courts? She also used my fiance's insurance after the divorce was final, knowing that she was no longer covered. We took care of that by sending the insurance company a copy of the divorce agreement, but it's just one more example of how she has lied and gotten away with it. Someone...please.....send some good advice our way.
Thank you