I've been wanting something like that (but honestly, better!) for a while. Tried to modify the forum leader page a bit, didn't get worthy results though. Please send me a PM when you get it working and on the forum!
Has anyone ever asked the staff here if it's a public mod?
--------------- Added 03 Mar 2008 at 2:56 am ---------------
And of course some searching found some more answers.
Someone's already done a mod that can do it (but it can certainly be improved):
https://vborg.vbsupport.ru/showthread.php?t=166085
It appears that the vBulletin.org one was done by the staff member Princeton.