Shoutbox

I've tried the obvious (Windows CBT hook), but even the HCBT_ACTIVATE doesn't seem to be triggered when the contact list is shown. I know a CBT hook would work if I had an EXE running before Messenger, but I'm writing a plugin, so all windows have already been created.
I know TazDevil is at least able to manipulate the contact list window, so I was wondering how it's done? And if anyone else has any info as well.

Ultimately, I want to add a menu to the contact list window.