It's a lot of bother, but I believe you can "extend" an award booking for two more weeks. Make a reservation and you get a two-week hold. On the last day of that two weeks, call and ask if they can extend the hold for another two weeks. (I have done this before with just one extension, however I did have plenty of miles in the account. I just needed more time to get the plans right.) I don't know for a fact that this plan would work, but it seems like it would as long as you never let the "hold" period expire.

Edited to add: wow, posting almost the same thing at almost the same time as Flailey. That's scary!