I visualise a pair of lips for this particular piece and am in the process of creating said lips.
Created a map of lips to help me decide on the perfect shape along with possible mouth poses.
I plan on using Zbrush to flesh out these realistic to be looking lips~
I also found a rig I'd like to use in making the lips sticky (lips slowly parting etc) I am quite excited in getting that to work so I'll try a couple of tests first then apply it to the lips.
Sticky Lips Deformer by Chad Vernon