Hey Henry, I think the feature you're looking for is "treat a sheet like a data source", and that specific feature isn't in Tableau yet. That said, there might be more we can do on the data modeling side, or with dashboard actions that might be able to give you the behavior you're looking for...If you could give me some more info about the schema of the original data set maybe I could help? Does your data set look like:
Revenue April 2016
CoGS April 2016
Or are your data sets crosstabs, similar to the ones in the attached spreadsheet?