My sister can drive with her knee. I cannot. I did try a couple of times, but I can't seem to get the same control as she does. I'm putting this up to the fact that she's shorter than I am, so sits closer to the stearing wheel, so must curl her leg up differently and is at a better angle than I could ever achieve.
Really I just tell her it's dangerous, because I can't do it so I don't want her to do it, either. But I can admit this.