Your footage probably doesn't support this, but I though maybe a trick to try would be to use the color picker tool on just the lip color to make the lips the source of a moving matte... essentially chromakeying using red lip color instead of blue or green. Use a tight multipoint garbage mask around the mouth to help filter out similar color. That key could then drive lips of any color you want when appied to cut a key with another solid in the comp... but I'm not an AE guy (yet), just musing out loud...
What you're trying to do sounds lots like the old "synchro-vox" technique from the
Clutch Cargo and
Space Angel cartoons of my youth in the early 60's.
They used to parody this effect on Conan O'Brien. But the synchro vox as I understand it was based on luminance keying of people wearing high-contrast makup around the mouth and lips. It was a technique developed to speed the proces of making saturday morning animated cartoons on a tight schedule without needing to hand-draw and ink a lot of key frames for the dialogue scenes.
