Kai,
You don't have to be Kaspar Hauser (a notorious fraud, BTW) to encounter the problem you pose in your thought experiment. "Knowing what it is like to be a bat", or anything else, if it is possible at all, would be possible for only one kind of of being: a bat. Thomas Nagel never suggests that we or anyone could "know" what it is like to be a bat. On the contrary, he selects a bat for his example just because it's echo-location-based means of perception is so vastly different than our own. His main point is that, in spite of the fact that we can never "know what it is like to be a bat", it must be like something to be one. Even the bat does not "know" what it is like to be a bat. Yet it still must be "like something" to be one. As it must be like something to be a flying squirrel, a bird, a horse, a chimp or a homo sapiens sapiens. 
It is possible that consciousness is simply "what it is like to be" a particular species of animal. Thus, it would not be a kind of knowledge at all. Consciousness, on this theory, is a condition of being that is caused to be what it is by the specific kind of electro-magnetic activity generated by the brains of animals of that species. The various qualities ("qualia" or "phenomena") we experience in perception are the ontological effects of being an animal with a brain. That is why these qualitative appearances seem to us to be objects of knowledge that are the causes of our behavior.

Consciousness (i.e., having qualia) is not the same thing as rationality (i.e., using language). Both are caused by the brain, but in different ways. Rationality and perception are functions of the brain, selected in evolution because of the kind of work they enable. Together they can explain all of human thought and behavior. What they cannot explain, though, are the phenomenal appearances of qualitative states of consciousness as non-public, immediately present, objects of knowledge that are, somehow, reliable representational images of objects in the world. But this is an illusion caused by the fact that it is like something to be an animal with a brain. Another way to say this is to say that qualia are intrinsic (or subjective) rather than extrinsic (or objective) properties of brains. But these intrinsic properties do not supervene on the elementary particles that constitute the animal body. They are identical to those particles, as they have been shaped by 100's of millions of years of biological evolution and a few thousand years of cultural evolution. Thus, consciousness is seen here not as a supervenient property but as an intrinsic one. By taking this ontological approach we avoid the illusion that qualia are special objects of knowledge. Insodoing we also avoid the conundrum, inherent in your analysis, that "knowing what it is like to be a bat" raises the question about how we know about the levels which supervene upon the elementary particles of a bat. Knowledge of particle physics doesn't explain consciousness any better for a normal human being that it would for your hypothetical Space Kaspar. 


Finally, I don't believe particles physics explains the 2nd law of thermodynamics (entropy), either. That is another topic. But it is related to this one in that it points out that the postulation of supervenient properties is always problematic in that these properties are not physical, yet they are taken to explain changes in physical bodies and processes. How can a non-physical property possibly be a functional property that causes things to happen in a world that is constructed entirely out of elementary particles? Indeed, the Standard Model of elementary particles lacks anything to explain why particles or the composite objects they constitute, have mass. The omnipresent Higgs boson is postulated for this job but still has not been found anywhere. Confidence at Cern is reported high for an answer as soon as this year. But, to date, a thing that is supposed to be everywhere has been found nowhere. 

Your thoughts in reply are welcomed.

dcd