MDX Cumulative Measures from specific point forward,

Hi

I have a cumulative calculated measure (See below)

However, I need this to ONLY start calculating from a specific dimension member onwards. for example the measure group table is linked to a dimensionand only when a certain flag = true must it 'start' computing the cumulative - is this possible?

Also I found that when I apply dimension filters the below cumulative measure does not seem to take them into consideration?

SUM
(
{{[DimFirstPayDate].[First Pay Date Hierarchy].CurrentMember.Level.Members}.Item(0):[DimFirstPayDate].[First Pay Date Hierarchy].CurrentMember}
*
{{[DimAsAtDate].[As At Date Hierarchy].CurrentMember.Level.Members}.Item(0):[DimAsAtDate].[As At Date Hierarchy].CurrentMember}
*
{{[DimContractFlagsByPeriod].[Period FPD].CurrentMember.Level.Members}.Item(0):[DimContractFlagsByPeriod].[Period FPD].CurrentMember}
, [Measures].[Loan])

I.W Coetzer