I doubt that it's completely done, putting it in front of a window and using campden might slow it down, but won't stop it. Also, if you add sugar to it, if you plan on sweetening it, it'll start right back up again. I wouldn't consider it done until the SG gets to between .990 and .996 or so, and it doesn't lower any more. Again, it'll clear when it's finished. Brown sugar or no, it'll still clear once fermentation is over and it's ready to clear.