Was gonna request this, but will look into the parameter thing. Thanks.
My reason is that I do boot-time defragmentation and if I can clean out temporary files on shutdown I can let the boot-time defragmenter work on all files.
EDIT: Hmm... it seems that it can shutdown after cleaning, but what is meant here is, that it runs before shutting down. In other words, if I go to the start menu, click turn off computer and then shutdown, then it runs before shutting down.