I find it hard to imagine anything other than the following, though it's speculative. If a man can convince himself that he has achieved "mature purity" and "domination over concupiscence", and if Christopher West is saying that "custody of the eyes" is not an issue for such a living and breathing saint, then it simply follows that such a man would do the rather naturally sinful thing of looking at naked ladies - maybe even at porn. I don't quite imagine what such a man would do once the inevitable sexual arousal occurs, unless he really manages to tell himself that he's appreciating the beauty of the naked body "without shame" and that his physical symptoms upon doing so are not lust but a "seeking of God."
It's Gnosticism. It's the Illuminati all over again. If a pop-TOB devotee is "in on the know", if he has the special esoteric illumination, if he's achieved "mature purity", well looking at naked ladies for him is not what it is for you, you vile beast.
Meanwhile, "Naked without shame" is such a strange concept to me. Chesterton points out that not only is nakedness shameful in fallen man, it's positively un-natural. What was natural in Eden is not natural now. Clothes are now a part of the nature of man. Since the Fall, the first thing one should do to get "back to nature" would be to put a pair of pants on.