Yes, but all they needed to do was kidnap him. Forcing him to become an unwilling and controversially under-age participant in a tournament which could have resulted in his death (possibly they could have got some blood from his corpse, but I suspect the spell specified fresh), and then fixing the tournament to make sure he won it, seemed unnecessarily complicated. As my friend said, they could have turned his toothbrush into a portkey, and it would have worked just as well; the goblet didn't appear to have been one until it was enchanted while being hidden in the maze.