Does anyone have any experience with creating custom NER for DBA Calculations?

We are considering creating custom NER for DBA calculations (to be set up in the P07901 DBA Calculation Control File) for a specific need.  We would like to know if this can be created as a separate new BSFN, or if it MUST be created within the N0700003 BSFN in order to function properly?  And does it have to be in the CPAY DLL?  We would rather avoid altering the standard JDE objects if at all possible. 

Any information would be greatly appreciated. 

Thank you!

Carmen