You and your wife are in the driver's seat here. The ONLY way that he can claim her as a dependent (for 2010 or 2011) if you file a joint return is if the ONLY reason that you file is to receive a full refund of all federal income taxes that were withheld from your wages AND you both would have had $0 federal income tax liability on separate returns.
If your income is less than $9,500 it won't hurt to file MFS and let him claim her. If you earned more than that, you WILL owe tax. If you earned the filing requirement amount for a joint return ($19,000) you'll owe $1,000 if you file MFS or $0 if you file MFJ. The more that you earned, the worse it will be for you.
If you and your spouse file MFJ, his claim will be denied as a matter of routine if your income is over $9,500. There's NO way that he can force you to file MFS.
If you want, offer him a compromise if your spouse agrees. Figure your taxes both ways and show him how much more it will cost you. If he gives you AT LEAST that much UP FRONT, file MFS and he can claim her. If he refuses, file MFJ and let him fuss.