Sell a phone and remaining payments of AT&T contract?

So I have a Galaxy S5 that was on the 18 month AT&T Next 18 plan. I recently purchased the S6 Edge and am now paying monthly on both.

For the S5 I was on the 11th installment of the 18 needed to complete the payments (24 to pay off the phone entirely). I was wondering if, since I currently don't use it, I can sell the S5 to another AT&T user and transfer the remaining balance to their account so they can pay monthly on it and it will no longer be tied to my account.

Thanks.