The answer to whether you can have the seller pay the 2015 dues is that you can do an agreement under which you estimate what those dues will be and agree to have that as a deduction to the total sale price either up front or at closing.
What you do not want to do is simply have the seller agree to pay those dues when they become known and due long after closing. You want a closing that results in neither side having any obligations to the other once the closing has happened. You do not want to be in the situation where you may later have to chase after that seller to get him to pay the 2015 dues for which Disney will consider you the liable party and you would have to pay them and seek reimbursement from the seller.