Presuming that you're using the Unreal IRC'd, why not just use the Global command to send to everyone on the network, rather than each channel. If you're not using Unreal, check the documentation for the IRCd that you do use for something similar.
As far as sending to all channels, I was unable to find anything in the Unreal documentation that would allow that possibility. Again, if you're not using the Unreal IRCd, then that option may exist for you, but I don't have the information to be able to write the script.
