xinetd: is it possible to bind service to all interfaces EXCEPT one?

I have previously asked this on ServerFault, but since it seems to get little views there, maybe there's a chance it will be better answered here... (I have deleted the post in ServerFault as indicated in the comments). I have a service that is running under xinetd. My server has many network interfaces, one of them is connected to external network and all others are connected to multiple internal networks. I want the service to be available to all internal networks, but not to the external one. Is it possible to do it in xinetd.conf file somehow? The "bind" option seems to do exactly the opposite: bind service to one particular interface, but not to the others. I cannot list all the interfaces (except one) explicitly in the config file, as the interfaces themselves and their IPs can change (most of them are VLAN interfaces that are added/removed on the fly). Or is the only method to firewall out the service on external interface with iptables or similar?