Select the row of polygons where the upper and lower jaw meets, do a smooth shift pushing the polygons inside the jaw a little, repeat that as many times as necessary to form the throat. Remember to check if the newly created polygons belong to the head body group ( in lightwave you declare them as a "part") before you export to obj other wise the head bone will not move them with the rest of the head. Make all your morphs for open mouth etc... as endomorphs within lightwave and export them.

Dominique Digital Cats Media