Collections Aging by Collector 7 Bucket Report

Summary: I am having to customize the "Collections Aging by Collector 7 Bucket Report" to add a DFF (Attribute) from the Invoices table (ra_csutomer_trx_all). The DFF value will have to be displayed next to the Invoice Number on the report output.
I copied the seeded report's Data Model into a custom one and it looks like most of the fields on the report are being derived from the seeded PLSQL package AR_ARXAGMW_XMLP_PKG. There is no documentation available to view the inherent procedures within this package.
Have anyone come across a similar requirement of customizing any AR Aging report and deriving additional values from the seeded package AR_ARXAGMW_XMLP_PKG? Answers to similar questions on this particular report are not clear.