Campy, I read the same article, and agree with the premise that inferior ramus spacing is the more useful measurement -- once getting into a pelvis rotation similar to that on the bike.
I was able to measure by placing a dry paper towel over a damp paper towel on a low surface (toilet lid), crouching similar to riding position while hovering over it, and then briefly touching down.
It leaves two damp divets you can measure. If you repeat the measurement more upright, the space between divets increases as you have rotated the pelvis back,which widens the boney contact points.
My wide ass fits the narrow fizik well due to the rotation.