I agree with @DJDonovan .
When I deploy them I generally create a template and allocate a prefix of address space for them all to sit inside of (for example, a /16 of address space will support 256 Z3s each with /24 subnet). If you don't need to talk to the LAN of each Z3 - you only need them to be able to talk to your network - you should be able to use the same subnet at every site (just don't include it in AutoVPN, and it will get NATed).
Then all you do is create a new network, attached to the template, add the Z3, and you're finished.