If you are already using blendshapes to create faces, consider one more blendshape face in your group that you can rig up with clusters, or lattice points, or even a collection of joints where you want the added control. That blendshape face can be defaulted to neutral and you turn the blend up to 1 forever. As long as nothing changes, you'll never notice anything. But once you manually change the clusters or bones, or whatever, you will have added control on top of the regular blendshapes you created. If you build extra control curves for them, you don't need to ever look at the original blendshape.
These controls can be anything from a tiny twitch in the lip to very cartoony squash/stretch shapes.
I see you are using an icon from Jason Osipa's "Stop Staring" book. If you have the second or third edition, there is discussion on creating very extreme types of facial deformations using additional blendshapes so that it never hurts the actual head on the rig.
Good Luck!