The castor oil pack is applied directly to areas in question - so wherever the cellulite is. :) It can also be applied on mainly the right side of the abdomen to help the liver, which indirectly aids cellulite.
You can make your own castor oil pack or buy a pretty nice setup from the Edgar Cayce cures catalogue from Heritage store - I forget the exact name but I think I left a link in the post in the FAQ, and there's a link on usage etc in that post. :)