How can I get YTD for a specific member of a NON time dimension

I'm trying to create a calculated member in my cube the will return YTD for a specific member of my Account dimension and don't understand how to do it.

//This calculation works great.
//It returns Per Square Foot average calculation for Account member 8 (Mark Yield Shipped) or my Account Dimension. 

CREATE MEMBER CURRENTCUBE.[Measures].[Actual PSF]
 AS 
       ( 
         [Measures].[Actual] / ([Accounting].[Accounts].[Account Level 01].&[8], [Measures].[Actual]) 
       )
;

//My question is how do I get a YTD and Prior YTD for the above calculation? 
//The first SUM of the calculation works because it returns YTD for Actual measure, but the second SUM doesn't work for Account Member 8 filter because PERIODSTODATE only takes two arguments. How to show that I only want to get YTD for my Account Member 8?

CREATE MEMBER CURRENTCUBE.[Measures].[Actual PSF YTD]
 AS 
       ( 

	   SUM(
		PERIODSTODATE([Calendar].[Yr-Per].[Year], 
		([Calendar].[Yr-Per].Currentmember)), [Measures].[Actual]
               )

	    /

	   SUM(
		PERIODSTODATE([Calendar].[Yr-Per].[Year], ([Calendar].[Yr-Per].Currentmember),
			[Accounting].[Accounts].[Account Level 01].&[8]), [Measures].[Actual]
	      )
       )
;