After seing a post from Rene Bui on the POV-Ray newsgroups, I was encoruaged to try it again. He atempted the classic approach to sub-surface scatering (SSS) with POV-Ray (media and interior fading), and the results were very good. But it looked a bit waxy, as it’s always the case with this technique.
Thinking about it, I figured that the wax look it’s not really a direct consecuence of the technique itself, but rather a logic effect of having a perfectly hollow object, where all the interior medium has the same density. So I tought that at least puting a rough skull inside would help to get ride of the wax look.
But my skills at modelling are not enough to quickly create a skull, so I downloaded some from the internet for a quick test. Unfortunately, the only one I was able to import on Wings3D was an incomplete one, with only the upper-front part of the skull really modelled. But it was enough to test my idea, and it seems that I was correct, although it would need a full skull and some muscles for a totally convincing effect.