I'm actually not back. I've decided I like it too much here and have just settled in for now. But, I do occasionally have some time off from playing and get around to posting.
I think you would have to write some code that would basically say "if the forumid is x, then add [vB4] in front of the forum title. Or, if the forumid is y, then add [vB3] in front of the title" I would guess that you could do this in the plugin that puts together the information in the first place. What hook that is is something you should either look to find out, or ask in the modification thread about.