Power BI Calculation Group subtotals

I ran into this same issue today (3 years later) and managed to find a workaround, which is: more calculation groups. To solve my problem, I just added a new calculation group where each calculation item is 

Item = CALCULATE(SELECTEDMEASURE(),[Category] = "Item")

with one total category which is just

Total = SELECTEDMEASURE() --(or using a CALCULATE() to aggregate specific categories together)

I was then able to add this as well as other calculation groups as different levels of a matrix column hierarchy.

This workaround assumes two things: 1, that you have a manageable number of different categories to work with and 2, that your categories are static enough that you don't need to constantly update the calculation group. It doesn't appear that you can individually format calculation items, so this still won't look like the default Totals column, but at least the numbers are there.