How to Rig to the face

Hey I'm working on a medieval engie set, and I've made a chain-mail hood/helmet for him. I've tried to rig it to his head, but I'm getting some clipping errors. I haven't textured it yet, I don't want to move on till I've solved this issue.( I'll post a picture later.)Anyway, when he moves his mouth it clips, and I don't know what bones to rig it to because the facial bones aren't on the body model.( I'm using blender.) Does anyone have any advice? Thanks.