Wah Lum's Elbow To Toe exercise is, for those that can do it, actually supposed to be Chin To Toe. Similar to the stretching seen in the clip you linked but done in the standing position.
Although our high kicks are with the toe I've always been flexible enough to reach the chin with my heel.
Edit: WL seems to change things when they're too difficult for most students so I would suspect it was probably in our forms but changed to Toe Kick when noody could do it correctly. Just like Elbow To Toe changed from Chin To Toe.