What if you mount 3-5 LED's at the top of the eye holes shining down and aimed slightly forward toward a blue-tinted piece of plastic (from cheap sunglasses maybe). Since the light of the LED's would make it hard to see out of the eye holes, maybe use some black masking over the LED's (where they are above the eye holes and place another lens behind the blue-tinted piece and just behind the row of LED's. If this last lens was made of a piece of mirrored sunglasses lenses, then it SHOULD reflect the remaining LED light toward the front of the helmet (through the blue lens-covered eye holes) while allowing the user to see out the ENTIRE eye hole (rather than a slit at the bottom of the hole). The mirrored surface of the lens would also mask the user's eye's, so from the outside the observer should only see an illuminated blue-tinted lens from each eye.
I've not tried this, so I it's only theory. :unsure