parameters with LoV : how to print LoV desrciption (not value)

Question

I have a report parameter make with a Lov  (list of stores : id and description)

ID is used to filter the DataSet (in KA server).

In a birt report I want to print the store-description.

params['Store'].value returns obviuosly the ID.

params['Store'].displayText works only if the DataSet is local to the report, but prints "null" if the DataSet is taken from the Knowage server.

How can I do that ?

thanks.