OS X :: Airport Extreme - How To Configure Guest Networking

Background: I have a long background in computing and networking, but am new to the specific operation of the Apple Airport Extremes.

I have a network with an existing router in place that connects to the internet, and provides DHCP for the network. I want to add (potentially many) Airport Extremes to this network to provide two basic functions:

1) Wireless access to the existing network over a large office area (preferably on the same subnet as the existing, wired network, with the current router [NOT the AEs] providing DHCP services) and

2) Guest network access such that users joining the guest network can access the internet, but NOT any of the addresses on the main network.

I can find no way to do this trivially. It seems that if I set the AEs to BRIDGE mode, the option to set up a guest network disappears (perhaps reasonably so, since the AE would need to be able to manage the address range for the two networks).