Just a suggestion (although it looks a little like you may already be doing this)... there's nothing keeping you from creating a transmap for the skull-cap and useing that to 'cover the scalp' with hair underneath.

Cinema4D Plugins (Home of Riptide, Riptide Pro, Undertow, Morph Mill, KyamaSlide and I/Ogre plugins) Poser products Freelance Modelling, Poser Rigging, UV-mapping work for hire.