Provide dimension filter in measures

[SP1709]

Hi,

I am looking out for a way to provide filter for dimension in calculated measure.
In our data model same measure is used for storing all values. We are having Tag ID to identify what value is present in the measure
e.g
Tag Activity
ST 10
OB 20
OF 30

So if Tag is 'ST' then activity reprsents ST
if Tag is 'OB' then activity reprsents OB
if Tag is 'OF' then activity reprsents OF

So in my cube there will be three calculated measures say ST,OB and OF and one normal measure Activity
Tag is our dimension

Now I want to design calculated measures as
ST = iif(tag=ST, measure.activity,NULL)
OB = iif(tag=OB, measure.activity,NULL)
OF = iif(tag=OF, measure.activity,NULL)

Please let me know if its possible to provide filter on Tag dimension in calcualted measure. Any tip on this will be of great help to me.

Thanks,