Never got a response, but I figured a way around this. It required creating a couple additional data tables outside of Tableau to make it work. Here's what I did (in case anyone else ran into this problem or was curious.
- Duplicated the original data tables to create the needed aggregate denominators outside of Tableau. This allowed me to create "group" denominators for the demographic segments that would ignore any demographic filters.
- Created a relationship table to left join all other tables. This prevented data permutations and ensured aggregate lines were calculating correctly.
- Used a parameter to filter the "group" and a quick filter to filter the demographic segment
- created a "segment filter" calculation [Parameter].[Segment Picker]=[Segment Group] for the "group" filter
- set the quick filter to show only relevant values
Since the totals table didn't have a demographic segment field, it was unaffected by any demographic segment filters.