wp_list_categories and Post

Hi, I will try to explain what I need / wish for / trying to hack :):
I am using WP as a CMS. Already built everything (used plug ins for languages etc’). Now, on my sidebar, I list all -children of main category :

– Main category (Tech Help) (Not showing on side bar)

(This is what I show on sidebar) :

— installation

— Tech Notes

—Tech notes for X
—Tech notes for Y

and then under those categories, admin will use posts.
Everything works great, when I am on a category page, I can see the hierarchy through the “wp_list_categories” function provide. The only problem, WP doesn’t recognize posts with categories, therefore, when navigating to a post under a certain category, the indication where we are is gone. Since the function “wp_list_categories” doesn’t recognize this page or the category parent of this post as one. Now I know it has to do with the fact that you can have multiply categories for a single post and that could be a problem, but in this case, there could be only one category to each post. I am trying to figure out a way where I can hack the “wp_list_categories” function to add the li ul class even if I an on a post page, maybe by sending the parent category of the post as an argument to this function, but this looks too complicated. Any other ideas?

Thanks