Matrix Issue with Dates and Slicer

Hi Folks, 

I am hoping to build the following visual with measures, a date table and slicers on a matrix.

I essentailly hope to use a slicer than you can select a  minimum and a maximum date and this will drive the monthly columns.  

However I would like one fixed column at the start that sums all the values before the minimum date (Pre Slicer Sum). 

Would appreciate any assistance on how to achieve the below results. 

I know that Matrix Visuals and Dates can be tricky.

Thanks, 

Brian