I somewhat understand what you are asking; however, doing it without a "client" or some interface seems to be impossible.
What we use is
EZIrc. It's for VB 3.7, but operates flawlessly on our 3.8 installation. It also carries over the forum username, barring a few random nicks that don't work on irc. We have the script customized to our theme and forum colors.
Then, we use BewareIrcd as our irc server, as we don't want our users to have access to other irc servers. It runs on our dedicated box, and allows us complete control of the user's experience.
Hope this helps.