If you have a ZoneDirector, the ZD can set up a guest network using a firewall at the AP level to control/restrict what LAN resources a client is allowed to access. However, if you have a standalone,this functionality is not available.
If your network is smart/managed and you have VLANs, you can still make an effective guest network setup using separate Guest and Internal VLANs and having one SSID per VLAN on standalone.
But if your underlying network doesn't support VLANs, I think you're out of options.