This ne peut pas be done avec le standard DNS resolution provided by *nix (and Windows AFAIK), you need votre own DNS server to do this. On *nix dnsmasq is le best choice for this, et you can soit run this on chaque workstation ou run it on a server et configure tous le workstations to use this.
/etc/resolv.conf:
nameserver 127.0.0.1
nameserver 208.67.222.222
nameserver 208.67.220.220
/etc/dnsmasq.conf:
server=/freenode.net/8.8.8.8
server=/freenode.net/8.8.4.4