Dimensional Data: How to dynamically set prompt value

[okh310]

Hello, within my time dimension i have something called "Current Fiscal Year" with one child member that is the current fiscal year.  In my report, I want to set the data parameter to this value. 

I am using the following code in my data item: 
set(#promptmany('Time','MUN','[Data Item]')#)

I have tried to create another data item that says something like "children([Current FY])" or "descendants([Current FY])" and inserting that into the [Data Item] value in my set above.  However, cognos does not like this, it says it's expecting a member or measure.  The only way I can get this to work is to hardcode the MUN of the current fiscal year into the [Data Item] slot above.

Does anyone have an easy way to do this without hard coding the value?  Thanks in advance!