Default Assignment DFFs based on department and department costing

Summary:

We have 2 DFFs in Assignment page Supporting Org and Supporting Company that need to be defaulted based on department. In addition we also want default expense account to be defaulted based on department (using auto complete rules)

The mapping between department and the values that need to be in the DFFs is available in department costing tables (Around 500 rows) we would like to use an SQL (Value Set) to get the mapping and use the "get string from value set" function to refer to the SQL for defaults. Could you please suggest how to use the "get string from value set" function to point to a value set.