Problems joining PER_PAY_PROPOSALS table to see who initiated a pay change.

Background:  We currently have a custom PL/SQL report that runs against the PER_PAY_PROPOSALS table to provide information about pay changes that occur in our instance.  This report uses the LAST_UPDATED_BY column to look up the User ID to see who updated the record. Unfortunately this column always returns the user id of the last HR person that approved the workflow.
Problem:  Our HR VP wants to know who initiated the workflow (ie supervisors, mangers, directors, etc) but this information is stored in the WF_XXXX and HR_API_XXXX tables. After reviewing ER Diagrams for work flow and HR_API tables, searching the ALL_TAB_COLUMNS table for ID or KEY columns, checking the referential tab in Toad for tables that reference or are referenced by other other tables, I've been unable to find any way to connect these tables.  PER_PAY_PROPOSALS only has a few ID columns, like PAY_PROPOSAL_ID, EVENT_ID (this column is always NULL), and PERFORMANCE_REVIEW_ID. Each one of these ID's that I searched ended