Update a Measure value based on value of different measure

Hi,

I have a scenario where i need to update my measure value at a dimension with a value of another measure at different dimennsion.

For example:

CustomerGroup(CustomerDim)      Quantity_Other                                   

Abc                                                   100    (want this value to show as 40)

Def                                                   200     (want this value to show as 50)

CustomerGroup(CustomerGroupDim)       Quantity

Abc                                                              40

Def                                                               50

Here I want to update the value of Quantity_other with value of Quantity measure. I have written a scope statement to achieve this:

Scope(measures.Quantity_Other,CustomerDim.CustomerGroup.members);

this=

//(measures.quantity,customergroupdim.customergroup.currentmember)  --tried this

//also tried below

case when CustomerDim.CustomerGroup.currentmember is CustomerDim.CustomerGroup.&[Abc]

        then (measures.quantity,customergroupdim.customergroup.&[Abc] ) --if i hardcode it to 40 works

      else (measures.quantity,customergroupdim.customergroup.&[Def] ) --if i hardcode it to 50 works

end;

End scope;

It doesn't work as expected and it either shows same value of 40 for both or shows blank value.

Is there a way we can achieve this? either by scope or any other way?

I know i can do it in relational world by joining both on customergroup and update value but i want to do it in cube.

Any thoughts appreciated.