Jeremy Waldron has recently offered a theory of the use of foreign law in american courts based on his interpretation of Ius Gentium. You can find the text on the Harvard Law Review, now available for free. What Waldron deplores at the outset is the lack of theoretical awareness displayed by both advocates adn opponents of the use of foreign law in American Courts.
As an antidote, he offerst the notion of Ius Gentium interpreted as a 'general common law,' that is a law that belongs to a global patrimony of reason and goes beyond the law inter gentes, that is the law stipulated by two or more parties in their own interest.
Following his interpretation of Ius Gentium, he recharacterize the kind of disagreement going on at the supreme court as one between those who see 'law as will' v. those who see 'law as reason.' To conclude he warns that even the latter category has to confront deep seeded problem concerning 'the rational relation between what we are wrestling with (our actual question) and what others have figured out (that is our patrimony of reason).'
Waldron's is still a very sketchy outline of a new theory of the use of foreign law. That said, any attempt to drive the debate away from the boring old grounds that divide, for example, Justice Scalia and Justice Breyer, is a breath of fresh air. I agree with Waldron that an underlying jurisprudence of the relationship between domestic law and foreign law should be worked out, as it is unlikely that many people will be convinced by authoritative assertions of what the framers would do in this case or, for what it matters, what we ought to do according to our best moral intuitions.