I set up a control panel, like the type used for facial animation.
Linked that to blend shapes and alpha maps, using the Reaction Manager.
When the control is at -100, show the inhale blend shape and normal map.
When the control is at 0 show the default shape and normal map.
When the control is at 100, show the exhale blend shape and normal map.
The Normal maps are in a Composite map.
So I just slide the control from one side to the next and back, to make him look like he's breathing.
I'll have to re do a bunch of the skinning on him btw, it got messed up when I started adding blend shapes. I separated the head from the body, so I can have morphs just for that part.
The modifier stack in max looks like this and it works from the bottom up.
Skin
Morpher = Full body blend shapes, breathing is here.
Edit Poly = Attach the body and weld the neck verts.
Morpher = Head blend shapes
Editable poly = Head
I didn't expect that to mess up the skinning, but whatever, do it over... I know better next time.