I'm not completely sure this works, but I just thought of it. It requires a good friend or you to have two accounts.
Blizzard's new program "Scroll of Resurrection" allows you to get a free month if you invite someone's deactivated account to join wow again, and if the invited account reactivates their subscription, the inviter gets a free month. So basically, if you cancel one account (and maybe let the time expire) and have a friend or your second account use the "Scroll of Resurrection" on the expired account, you reactivate your account and the person who invited you gets a free month.
Like I said, I'm not 100% sure this will work, but it sounds viable and it's worth a shot. (No I have not tried it yet)