Here is a link to the Takii seed company site about growing eggplant. On the left hand side you will see a video that is 4:15 in length. CLick on that one. At about 2:30 you will see them prune the plant down to 1/3 to a half. However they do not root prune.
Hope this helps,
Jeff
http://www.takii.co.jp/tsk/saien_movie/nasu.html