Create Virtual Relationship Between Measure in One Table to a Column in Another Table

So I have two tables I am trying to create a virtual relationship with. My date table has ID, DateLabel, MonthStart, MonthEnd, and my data table has a calc column called BLTC $, Proj_Finish_ID, and the measure I am currently struggling with. 

I am trying to sum up the total cost of dollars from BLTC based on my Proj_Finish_ID measure, which is dynamic. I have a slicer with High, Medium, and Low user selections that each has different multipliers attached to them. When selected, the Proj_Finish_ID measure will change based on the new projected finish date from the selected multipler. 

However, the sum from BLTC has to be based on that Proj_Finish_ID measure that needs to have a one-to-many relationship with my Calendar table since I am using the DateLabel column from that table for my visual. Therefore, I am trying to attach the Proj_Finish_ID measure from another table to the Calendar[ID] column. 

I can't seem to use TREATAS with a measure, so I'm not sure how to go about this so the sum of BLTC can be allocated correctly to the corresponding month, not just the same total for all months. How do I create this relationship?