Global Warming and Hurricane Impacts: A Hypothetical Scenario

Over at Prometheus, Roger Pielke, Jr., has an interesting post taking Kevin Trenberth to task for discussing how global warming may have increased Katrina's total rainfall and thus caused direct damage to New Orleans. Pielke doesn't think Trenberth can justifiably say this, although previously (I forget the exact link) I seem to recall that folks at RealClimate had defended Trenberth's back-of-the-envelope calculation. I don't know enough at this point to have an opinion about the validity of what Trenberth said. However, irrespective of Trenberth's claim, I do wonder whether or not it will be possible, at some point in the future, to directly attribute some fraction of a single hurricane's damage to global warming. We all know we cannot say GW caused a specific storm (that's where Time magazine went overboard in its recent cover story). And in terms of GW increasing storm intensity, that would be an effect that could only be measured as an average increase. You couldn't detect such a change in any single storm. But just suppose, for the sake of argument, that we find ourselves in a world where sea levels are 1 foot higher due to global warming. Could we not then say of a hurricane's storm surge that global warming had added a foot to it? I have a hard time seeing why not, but I am open to argument on this question.