I make them manually in Photoshop. You can use the existing maps to figure out the UV configuration. I don’t think there’s an automatic way of doing it barring baking the AO from a high poly xgen mesh or something.
The red channel is tinted by the hair color, so it should cover the hair root. The blue channel is an unsaturated shadow and is for the edges where you have clumps of hair occluding the skin basically.