Does anyone have any tricks for creating mouths for characters from the side view?

I mean - when the character's head is turned completely to the side so that their profile is visible.  In this case the jaw would actually open and close... which doesn't lend to the "sprite swapping" method very well.

I am thinking about trying to draw the mouth shapes over the top... it might look a little funny...

Anyone have any tips?

Here is an example image: