Data Exchange Loadrule - Export to File - How to export full year data instead of individual months?

Summary:

I'm working on a data export via a load rule (Data Exchange) to extract data from a BSO cube at aggregated levels directly to a flat file.

I want to aggregate several dimensions, including the Period dimension. While the Options/Filters window easily allows me to select parent-level members for every other dimension, I'm hitting a wall with Period.

The Problem:
When executing the load rule, the execution window won't let me select the Year_Total member. It seems to restrict Start- and End Period selections to level 0.

My Goal:
I need to export the data with periods aggregated (e.g., getting the