Hi there, Jennifer!
My advice to you: try calling Disney Dining at (407) WDW-DINE every single day, at least twice (morning and evening). There is nothing at all wrong with this approach; the Cast Members at Disney Dining know that high-demand restaurants like Be Our Guest will attract lots of Guests who will work diligently to get that table.
Check
the Web site often, too.
And if possible, do not be too locked in to a particular time to eat.
The more you try, the more likely it is that you'll hit.
And yes, when you are there, walk up every day to see if anyone has opted out.
But don't forget: the lunchtime offerings - no reservations required - are delicious, and the "enchanted rose" technology is definitely something to see in terms of service.
Have a wonderful time!
See you later, celebrator,
-Deborah B.