Original Hacker News discussion is here: http://news.ycombinator.com/item?id=149052

This contains I think the first reference to DH7, by 'tungstenfurnace'. He attributes the practice of strengthening an opponent's case before refuting the central argument to Karl Popper.

This practice is noted in Bryan Magee's Popper (Fontana, 1973) :

http://books.google.co.uk/books?id=6sw1GGBUYjkC&pg=PA91&lpg=PA91

What Popper aims to do, and at his best does do, is to seek out and attack an opponent’s case at its strongest. Indeed, before attacking it he tries to strengthen it [..]