Wouldn’t aggday last or aggday max solve this problem? If you cron it every hour and just tell beeminder to use the last/highest value in each day, you should be covered for any deadline.
The problem with this is that Beeminder cuts you off after 150 data points each day (per goal). I ran into this when I tried to count webpages loaded and solved the problem with this script that increments the latest data point.