How about having more than the normal number of ad slots.
But if possible a additional ad slot after every 200th post and its multiplier would be a good incentive for advertisers to bid high for this week.
Of course, you could automate it, but I'm pretty sure Theymos manually has to upload ads every week, and it says on the thread that it could be longer than 7 days, so it's not automated. In fact, it would be easier for him.