It could be done. I have the plan drawn out in my head, but not enough PHP knowledge.
You could just use the same principle that JoshPet showed me with having CSS independant folder icons on ubbthreads.php. You could either make a new cell, or just take out the post icon and put it in there as a background aligned left and non-repeating...then put the appropriate amount of spaces before the thread title so that it doesn't overlap.
Make sense?