Hm? It does solve your problem, at least it enables you to only change the brightness of the second skin with ambient where the rest of the model stays the same (apply a material to the model that ignores ambient and use ent_mtlset to apply one that uses ambient to the second skin).
"Falls das Resultat nicht einfach nur dermassen gut aussieht, sollten Sie nochmal von vorn anfangen..." - Manual
