Poselib slider?

Is there any way to make an armature (or anything) in a way that mixes poses in a pose library?

I am thinking of a “driver armature” that drives poses on a more complex armature, namely for facial animation with bones.

Rotate bone - Increase the smile
Roatet another bone - mix in a jaw drop to end with an open smile

I know there is that addon that lets you create drivers for anything, but it doesn’t work in 2.78 and the pose doesn’t have a data path to copy.

Addon for mixing poses was attempted…
EDITED - that addon doesn’t work in 2.79. But check out Action constraint, it’s better than Driver and pose library combo.