Geez, I was being sarcastic. It was just an idea, I may not even be right about the feature being related to being away, but instead just idle.
This sort of feature would probably have to run on the server side. Maybe in the form of a list of all the nicks in the channel and along with each their away or idle status. Then the status of the nicks could be checked when you join the channel (if the mode is already set) or one signal set to the nicks in the channel once, when the mode is set/removed. I don't think this has to be a sort of thing where a client should have to be checking status every so many seconds.
Anyway, this would not be something that mIRC could do, but for the sake of the disussion, that was just what I pictured. I could be wrong though about how much even this method would affect the servers.
Thanks for the feedback all. At least I know now that it probably can't be done. At least with mIRC...
Thanks