Using cutter for mouth?

When viewing my “character” from the side, I want to have a small gap of nothing in the space where the mouth is supposed to be.
How do I remove the part of the head where some of the mouth will be, without changing the head itself? (like fake-removing part of it)
I know about the cutter, but how exactly do I use it for this purpose?

For example, how do I remove the part in the red circle?

I just need to figure it out for an animation I’m working on. Thanks!

There is a rig on Gumroad that has profile mouths which may help you to see how it is done in this rig.
He explains the rig and the mouth here:

I thought the forums would help me but after a month I see Toon Boom doesn’t care about the community.

Bump. Anyone? :confused: