Dataflows: use Workbooks as a source

I have never used the Workbooks section of an app workspace, but now I got the idea of using it for Excel users to publish their data to. It would be great if I could then use this data in a dataflow. I couldn't think of a way to do this. Does any of you know a nifty trick? I already created an idea because I am pretty sure it can't be done, please prove me wrong! :smileywink: https://ideas.powerbi.com/forums/265200-power-bi-ideas/suggestions/36137743-add-the-ability-to-use-excel-files-in-workbooks-as