Derive Expense owner's employee number in expense report

Summary:

Currently we don't have employee number in payment xml so we are trying out ways to bring expense owner's employee number through DFF

Content (please ensure you mask any confidential information):

Steps to add employee number on Payment File XML by defaulting the Employee number on Expense Report Header for the required Business Units ( Doc ID 2602232.1 )

Based on above document, Currently we have defined a DFF at expense report level (query below) which will auto populate the current user login's employee number. So once expense report is processed as ap invoice. DFF details are getting transferred from expense report to AP invoice.But here if we use delegation functionality DFF is still populating login user's employee number. We need to get the expense owner's employee number in the DFF so that the same reflects in the payments XML.