Yes, I've done it. Make it for 11 months from now. Experiment to get the correct amount or close to it. If you go over you will have to add new monies. Once you make the reservation wait a couple minutes and cancel it. You'll get a new voucher good for 12 months from today. By canceling that far in the future you won't be subject to any penalties. Plus, if necessary, you can push it forward again when it is close to expiring.