Ubiquitin,
I used the airplane example because it has a clear line between the two bits of evidence (the habits of businesses and the absence). Your elephant case is really the same thing. We know that an elephant ought to be visible in the room because we have a tremendous amount of evidence that elephants are very large creatures that take up lots of space. But because this is so obviously true we don’t think of it as a piece of evidence.
My point is that absence of evidence as evidence of absence will (logically) always require additional information, i.e. evidence of why we should expect to see the evidence that we do not see.