We have a client that had two cubes but they only want to load the GL data to stage once

The way I can think of is to have the Process step on the WF kick off a DM job that extracts and loads the data into the other Cube. However, the document attached has extracting Cube data, so you would need to write a BR to extract the Stage data instead. There is an example in GolfStream of an extender BR to extract Stage Data.