1) Make a short movie/image sequence with all your facial expressions on seperate frames.
2) Import your movie and apply as a decal to your model's face.
3) Create a new Action for your model and then expand your model's shortcut to get at the decal's "Timing" properties.
4)Go to frame 0 and set "Frame" to whatever frame of your movie holds the facial expression that you want your character to start with. Repeat for all frames, using double keying to hold frames or build whole sequences into your animated decals and let A:M interpolate between frames.
It is a very powerful and economical way of animating, especially suitable for anime.
I would like to be able to select the frames via a pose slider but I haven't worked out a way of accessing the decal's timing properties from a pose.
Good luck and post some examples.