Actually i wasent thinking freecamin in the head

It more like using transparency (.png files with no background in certain parts.)

Imagine this:
A face with with wide open mouth. Head texture is transparent down the trought ( surrounding teeth, tongue).
On the new texture u draw an eye or small face on the back of the head surrounded by dark red color with transparency in the front, where the mouth is.
That wad more like what i was imaginng.