[SirFlash]

binevi, according to vbulletin staff, vbulletin 3.7.0 already has this feature implemented, apparently you just need to "create user image_prefix now and create five pictures with the name prefixforum_old.gif and etc".

I haven't done this myself yet and i find that explanation difficult to understand, but apparently that's what you need to do. I'm not really satisfied with this solution personally, since i don't like creating new user ID's unnecessarily (since all new users have numbers attached to them in the URL), and i find the old Category Icons hack to be ideal since you can edit the icon directly in the Forums area, which is just downright intuitive. In any case, i'll try following their instructions and let you know if i succeed.