There's an option if you're willing to tie up some cash for a while. Take the one you just bought - presumably not activated - and put it away in a safe place. Then buy a new pass with the current promotion.
Sometime in the future, you'll probably want another pass. It's waiting for you in your drawer, where you safely put the one you recently bought. If the certificate is still fully valid, your annual pass is ready to go, and now there's no 13-month promotion that you're losing out on. If its past its validity date, it's still worth the money you paid for it - and can, I think, be used as credit toward any WDW ticket, including regular MYW tickets.
Yes, it means you have to buy one of your passes way in advance and tie up the cash. Not ideal, but it's an option.