If someone plugs into the network at the conference centre, do they have access to the network. ie can they ping all devices on your network ?
If they can, and you only want to allow them access to your internet gateway, you could setup an Access Control list, if your switch allows it.
If they can’t ping any devices on your network, then what ip address scheme are you/conference user using?
(They’ll either need a static address on the same network as the rest, or an DHCP assigned address.)
Hope This Helps.