DAX formula to calculate cumulative running total across two columns that halves on non workdays

[jeffreyweir]

Okay, so this isn't strictly a PowerBI problem, but rather a DAX problem that I'm trying to solve in PowerPivot./Excel, although we will be migrating the workbook to PowerBI in due course.

So here's my problem:

I have some data (90,000 rows) I'm trying to use to calculate a cumulative "fatigue score" for folk working shifts...currently using PowerPivot/Excel 2016.

As per the below screenshot, the dataset is shift data for multiple employees, that has a cumulative count of days worked vs. days off that resets back to 1 whenever they switch from one state to the other, and a 'Score' column that in my production data contains a measure of how fatigued they are.

I would like to cumulatively sum that fatigue score, and halve the cumulative sum for each line that Workday is FALSE. . My desired output is in the 'Cumulative Total' column far right, and I've used grey highlighting to show days worked vs. days off as well as put a bold border around separate Emp_ID blocks to help demonstrate the data. 

This is very similar to a question I asked previously at StackOverflow, with the difference that I need the cumulative total to halve every time the Workday value is FALSE. Alejondro came up with a solution to that problem that looked like this:

Cumulative Score =
CALCULATE (
    SUM ( 'Shifts'[Score] ),
    FILTER (
        ALLSELECTED ( Shifts ),
        [Helper] = MAX ( [Helper] )
            && [EMP_ID] = MAX ( Shifts[EMP_ID] )
            && [Date] <= MAX ( Shifts[Date] )
    )
)

...but I need to amend this to halve the cumulative total each time the Workday value is FALSE.

While making these kinds of adjustments to cumulative totals is very simple in Excel, I'm not sure this is possible in DAX.  Currently we are in fact using PowerPivot to serve up the data in Excel, and then using Excel to create the cumulative logic, and then pulling the cumulative totals back into PowerPivot via a linked table, which works but is clunky.