Sum base members by property for Parent node

Hi Experts,

we need to sum only base members marked with property for parent node.

Parent sum = 100  (only where property L1="Y")

base 1              20  (property L1="Y")

base 2              60  (property L1="Y")

base 3              20  (property L1="Y")

base 4              1000  (property L1="N")

We were thinking about following solutions:

1. different hierarchies [since it can be more properties and parents, a lot of hierarchies would be needed, also for combinations]
2. local members with dynamic formula or EPMretrievedata to simulate the parents [about 70 for one report]
3. script logic and extra members as parent's duplicates [script will sum it up and will be triggered everytime reports open]

has anyone developed other solution?

thansk,

tomas.