How do you think it will be portrayed in the movie?
I mean, in GR I it seems to me he "speaked" actually moving jaw, and the normal text bubbles were the same of Blaze, the difference was in the tone of speak (more imperative, ecc).
In GR II the black flaming engulfed bubbles made his words like they were coming straight from hell; i always imagined a riverbering, deep tone with echoes, (that was one of the coolest thing of the comic imho). And i think that because the skull was actually more realistic, the jaw opening wasn't in pair with text bubbles, meaning his words were sort of a telepatic communication. It would be a little ridiculous see his jaw muttering every word like a sock puppet...
Cgi orbital bones deformation would communicate quite some "expression", but jaw/mascellar bones deformation would look too cartonish...