After some googling... the previously-mentioned special provisions are in fact laid down in the Constitution (Grundgesetz) - article 116. However, going by the wording of the article it looks like on needs to move to Germany in order to apply.

Anyone wanting to go down that route will probably need to do some research on what is required in practice (e.g., whether one needs to be physically present in Germany for any length of time, or whether it is sufficient to register a place of residence with the German authorities)