Maintain a data structure for users, when a user speaks their address is given, so fill it in at that point (and on a whois, join, or any other appropriate event). If the user has not spoken at the point you wish to ignore them, issue a /userhost command. The server will respond with a raw 302. (I found this using /debug.) This is how mIRC appears to behave.
Thanks for the reply. I have spent the last few hours writing a structure that handles the WHO reply on join. Userhost was the command i was after.
I do have mIRC with debug on. But must of missed it and in the reply.