Tongue Out Detection with Blendshapes

Hey Lens Community,

I'm working on a new 3D model right now with shape keys in it for the face expressions template.  I'm wondering, however, if anyone knows of a script or anything for a way to detect when the tongue of a user is out so that the model can simultaneously extend its tongue.  My goal is to be able to make an additional shape key in my model for a "Tongue Out" position and whenever the user's tongue is out, the value of that shape key increases.  There's no tongue out position listed on the face expressions API page but I'm wondering if it's still possible with some scripting.

Thank you!