Stylevar conditionals?

I'm not sure how to phrase the title for this..

I've got a background image for forumhead_background:



I'd like that image to be different, depending on which forum it's the header image for. So if it's "Site news" it's forum #1, General Forums would be number 12 (whatever), etc, etc.

I think, that the VB3 way would have been a simple pointer to the forumid in the image itself, eg: "/forum/images/blah/header$forum['forumid'].png"

Since it's inside a stylevar, I'm not sure how to go about it this time. I'm looking to take my header image (catheader.png), and make a few version of it, so catheader_1.png for forumID #1, catheader_12 for #12, and so on.

Would I need to preregister all of those conditionals, or is there a way that I can just directly pull the raw forumid inline with the image ponter in the stylevar?

Something like this horrible syntax:

url(images/misc/catheader_<vb:raw forumid>.png)