Combining Data from Multiple Relational Data Sources into One Table in PowerPivot for Excel

I have read a tip on Importing SQL Server Data from Multiple Data Sources into PowerPivot for Excel, which talks about bringing in data from two or more sources into PowerPivot and storing data from each source table/query as a separate PowerPivot table. I would like to know if there is a way to combine data from two or more databases/sources into one table in PowerPivot.