Cisco :: 5508 Guest WLAN Dropped Off Outside Firewall

We are implementing a new corporate headquarters and have bought a Cisco 5508.  I have two connections plugged into the 5508 in ports 1 and port 2.  Port 1 is for all internally wireless networks and connects to our core 6500 and use an external DHCP server scopes.  Port 2 is for our guest WLAN and connects directly to a public network switch in front of (outside) the firewall.  For the guest network, I have setup a vlan on the controller for dhcp and the interface setup to that vlan and dhcp scope built on the controller. how or can I NAT the internally addressing for the guest network to  the public IP address on the controller.  Essentially I want to drop of guest network traffic outside the firewall and not have to deal with setting up the firewall for any aspect of guest network traffic.