Dynamically Ignore Slicer Interaction

I have pretty standard star schema relationship.

FactSales Table

• DateKey
• EmpId
• ClientId
• SaleTypeId
• GBPValue

Dim Date Table,

• Date Key
• Year
• Month etc..

Dim Employee Table

• EmpId
• Group
• Employee Name

Dim Client Table

• ClientId
• ClientName
  etc

I have a matrix set out like

Rows: Group > Employee Name > Client Name

Columns: Year > Month

Values: (Variable) Reporting GBP

I have 3 slicers on the page. 
1 is for the user to change the SaleTypeId depending on what they want to look at.  (Sales, refunds, pending etc)

2 single select year

3 multi select month slicer.

The (Variable) Reporting GBP measure is just a switch function

     VAR _s = VALUE ( SELECTEDVALUE ('FactSales[SaleTypeId]'))
RETURN
    SWITCH ( TRUE(),
            _s = 1, SUM(....

For the majority of selections i want the matrix to only show for the single year and x months the user selected on the date slicer.

There are 2 though that when selected, I want them to ignore the date slicer and show alll years and months. (still retain the sale type id)

So in the switch measure it would be something like,  _s = 2, [(£All Measure)]

I create the [(£All Measure)] measure and use ALL() but it still only shows the 1 selected year in the column on the matrix.  

It seems to show the overall total for all years in that one year, but I really wanted to pivot the data over all the years but the date filter seems to still be applied.

Is this scenario possible to work?