To do this I believe you would create a master zone named "." in your named.conf (comment out the default "." zone with the hints information). Then, create a zone file which contains a series of wildcard records for the IP that you want to have everyone directed to.
If other people will be connecting their own computers to this network for the meeting, then keep in mind that some people will use their own DNS settings (OpenDNS, Google Public DNS, etc.) instead of the DNS server issued by DHCP, so unless you're blocking DNS at the firewall there is still a way around it. An HTTP proxy server at your routing point might be a better solution if that is the case.