PowerPivot in Sharepoint 2010

Hello.  

I am trying to create a dashboard in Excel for Sharepoint 2010 in PowerPivot

I have a library for document sets, that are tied to a (custom) workflow.  The workflow assigns tasks.  

Basically, all I need is to have a count of the total number of document sets that are actively in a workflow, and the active task.  

I've got the data feeds pulled in from the task list and the document library, however, I can't seem to make the relationship, so that the task is tied to the correct document.  

Does anyone know how to do this?  

I thought about pulling in a datafeed from the workflow, but I don't see that as an option anywhere, which makes me think either this isn't possible, or (more likely) I'm missing something super obvious. 

Thanks!