I think your position is correct, WWW, that there doesn't seem to be any simple evasion tactics such as slipping, etc.
However, when I practice the Jong, there's a motion of a low side palm while working your way to the side... I find this a good time to practice the slip of the head, among others.
I see Wing Chun as a very adaptable system and the way I like to do it is definitely to combine such movements as those in sparring, etc.
On the other side of the coin, in most self-defense/scenario drills, covering centre and going through the front door works great for me without any other movements of the head, etc.
Best,
Kenton Sefcik
An ounce of action is worth a ton of theory. Friedrich Engels