To get this done, you have to modify your data model to add strings 'Previous Month' and 'Previous Year' to dimension. For getting metrics of above dimension values, need to concatenate their aggregated values to oringinal metrics table. And this procedure can become complex depending upon your existing data model structure.
But, as you have stated above, 'you are currently creating another table for two rows'. I would suggest you to go with the same and in order to export both tables/charts to same excle sheet, there is workaround available.
For this, you can refer below excellent post by Stefan WALTHER: