I agree with Erin, it is possible but depends very much on your determination and support you will get while trying it. I would probably try to find a LLL leader in your area or a lactation consultant to help you out with this.
I have heard of women relactating many months after they weaned their babies, for different reasons, one among them was to nurse an adoptive baby. I have hear of women who started lactating without even being pregnant by solely pumping. So, as you see, it is definitely possible but it may require patience and hard work.
Whatever your reasons, I wish you good luck!