You might try doing a search for "ignore" in all mod titles, if you haven't already. I tried but didn't look at all the results. I did find this:
www.vbulletin.org/forum/showthread.php?t=109543 which looks like what you want but has some posts saying that it doesn't work with vb4, but I was thinking that it may just be that the plugin code needs
as the first line. (And if you try it and get it to work, post that in the mod thread).
Of course you probably realize that a user will always be able to log out and see the other user's posts, so there isn't any good way to completely hide them (unless your forum isn't public).