How do you transfer the Egyptian god cards from Yugioh Nightmare Troubadour to Yugioh World Championship 2008?

Unfortunately, no previous YGO! DS games can link with World Championship 2008, so you cannot get the God Cards from Nightmare Troubadour. I know for a fact that "Slifer the Sky Dragon" was offered as a downloadable card for one day, so perhaps that is the only way of getting the God Cards. yes ghosts exists.