Project Billing Invoice line description as expenditures Comment Possible?

HI , I would like to use expenditure item comment to be populated as projects Billing invoice line description.

COuld you please let me know where and how to approach for this customization please? Its bit urgent.

I use work based revenue and invoiced methods. System populates project billing invoice description as per Invoice format setup, where we dont have much flexibility to have invoice line description as per our requirement.

We also use intercompany billing invoices features.

So I require this customization for Projects invoices and PA Internal Invoices to work for.

Thank you so much for your time and assistance.