The Scrum rules say that all Sprint items need to be "fully tested, potentially implementable features" at the end of the Sprint to be considered complete. Sprints ALWAYS end on time, and the Team doesn't get credit and isn't allowed to present anything at the Sprint review that isn't complete - and that includes QA.
Technically, that's all you should need. A Team commits to a certain amount of work, finally gets it to QA two days before the end of the Sprint and the QA isn't done in time. So the output from the Sprint is zero, they have to go in front of the Customer and admit that they have nothing to show for a month of work.
Next time round, you'll bet that they'll pick less work and figure out how to get it to QA so that it can be finished on time.
