Overlapping Slicer

I'd do a disconnected table/switch combination that looks like this:

Step #1 Create a disconnected table:

Number    Chooser   

0               YTD

1               Last Week

Step 2 the measure

= Switch(min(DisconnectedTable[Number]),

0,[Calculation #1],

1,[Calculation #2])

Step 3. Bring the Chooser column, from the disconnected table, on to the pivot as a slicer. When you select YTD, the min will filter to 0, and the switch will run calc #1. When you select Last Week, the min will filter to 1, and the switch will run calc#2

Essentially you make two distinct calcs, one that does YTD, and another that does last week. Then the switch will toggle between them. 

Does this help?