In SSRS, aggregate measure based on dimension value

I am writing an SSRS 2012 report whose data source is an SSAS cube. In one table of this report, I am using a very simple data set with one dimension (Category) and one measure (Sales). The dimension has 4 members, A B C D. For the purposes of this report table, I want to show the sum of sales for A, the sum of sales for C, and the sum of sales for B and D combined. I then want to show each of these 3 values as a percent of the total (sum of A B C D). The data set looks like this:CATEGORY SALES ------------------------ A 10000 B 14000 C 8000 D 8000The resulting report table should look like this:CATEGORY SALES % OF TOTAL ------------------------------------- A 10,000 25.0 B+D 22,000 55.0 C 8,000 20.0 ------------------------------------- TOTAL 40,000