Forums mIRC Help Whois Information after the user quitting

I run a channel where we maintain a website that we change the password on a weekly basis and we put the new password in the topic for our users, so only the users of the IRC channel have access. Well ALOT of users will join the channel, get the password, and then part right afterwards. I was wondering if there is a way to get a persons whois information even after they have already quit the server, so I am able to add their IP to the banlist. Any help would be appreciated!

Maybe this works: /whowas nickname

While a /whowas may work, if you're going to be doing this on a regular basis, you might want to start doing a /whois on joining the channel, then storing the IP for a few minutes so that those that stay have the IP removed automatically, but those that leave quickly have the information stored permanently.

This would require more of a code than the /whowas command, but does have advantages.

BTW: Personally, I never would've started putting sensitive information into the channel topic, as the channel topic is displayed in a /list (unless the channel is marked Secret or Private)