RescueTime also has a custom goals-for-the-day feature: you set Time Filters (under Advanced Filters) during which data counts toward your goal. Say I set a time filter called “workweek” that ran from 8-6, Monday thru Friday, and set goals for 6 hours of All Productive Time, and 3 hours of Very Productive Time, that only accrued during those periods. RescueTime already gives me alerts when I hit that goal.
Would it be possible to add an integration where you increment a Beeminder goal if and only if RescueTime logs a goal met event? This could be a potential workaround!