Slurpee, what do you mean with in it? Part of your hack?
It should work if ubb_forum_summary.cgi is called before your hack is displayed.
Did you try to put the variables in your forum_summary template? That works definitly on my board, I can set it into a HTML comment to show you.
mark99, I updated the hack (before you did your post) it works now independent from the way categories are displayed.