Hi Helen, this does not appear to be the case in 1.9.3. Once the show rank is selected in ADMIN settings it shows up in all the classes and there doesn't appear to be a toggle in an individual course grade book to turn it off.
I did notice that 1.9.5 which you demoed does have the toggle so I will be anxious to start using that version.
As I said in my original post, the "politically correct" solution would be to have each student have the ability to toggle show rank. I am trying to get our local PHP code warrior to take an interest in writing a hack for this.