It's not what you're looking for...
But you CAN tell the controller software to send keystrokes at different rates. So you can kind of simulate it with the knob by using arrow keys at various rates. It's not "jkl" controls by any means, but it's better than nothing.
Hmmm...QuickTime does allow you to programatically set the playback rate...how about an AppleScript that changes the playback rate of the foreground movie, triggered by a hotkey, or by the controller?
--DAvid Althoff, Jr.