Hey Rob, the movement of the tongue Will not facilitate the change in lip shape.
Lip trills are a change of pitch. There is a common misconception that the change in tongue position will change the pitch by varying the speed of the airflow; this is simply incorrect.
I highly recommend going and watching and also completing the harmonic slurred challenge that I did over five weeks to become really familiar with the feeling of harmonic slur changes. There is a whole lot of information in the lessons.