You're planning to have a removable partition for the aviary so you could let them breed in the partitioned-off area. If that wouldn't leave enough space for the non-breeding birds, maybe you could make a separate, portable aviary for temporary uses like this.
The construction style that I used for my aviary would be useful for this - each wall and the ceiling is a separate module and they're attached to each other with straight brackets. To take it apart you just unscrew the brackets, and the pieces can be stacked flat against each other when they're not being used. You could use a plywood floor like I did, or you could use concrete "stepping stones" like these:
http://www.homedepot.com/b/Building-Mat ... 5yc1vZarm0 This temporary aviary obviously wouldn't be attached to the ground as securely as the real aviary, but you could drive some kind of stakes into the ground and secure the aviary to them for extra safety.
The portable aviary would come in handy in other situations where birds have to stay somewhere else for a while.