How to export layers separately while maintaining a bevel with Volume Object node?

This one seems complicated, so I hope you’re up for the challenge, but maybe it’ll be easy for someone here.
I’ll try to explain this as clearly as possible, and I shared a screenshot of my node view setup.
I created a vampire character, and his facial features are broken up into different layers; head, eyes, mouth, ear.
I am using the Volume Object > Normal Map > Light Shader nodes to achieve my lighting effect.
The ear and head layer are connected to the same Volume Object node in order to have a seamless lighting effect, but I want to export those layers separately. If I turn one of the layers off to export the other, the lighting changes. Both layers need to be on to have the seamless lighting effect. So if I am trying to export the ear layer, I turn the head layer off, but then the lighting on the ear is affected.
Does this make sense?
Is there a way to maintain the lighting effect while exporting the layers separately?
I thought maybe if the head layer was on but the transparency was turned down it would work, but it didn’t.
I hope there is a way around this. Any experts who can weigh in?b