Candidate Expense and Requisition Expense

Content

Hello.  I'm having some difficulty with assigning expenses to  candidates as well as I would like.  Primarly most of my leads are  driven through external recruiting sources.

As such, when I enter an expense in for a particular candidate I  would like to be able to assign the expense to BOTH a requisition, as  well as a source.  But the picklist only allows for TYPE, REQUISITION.   Is there a way to alter the picklist so that I can also assign a source?

For example, say I have candidate A.  He is hired, and comes from an  external recruiting firm.  I'm charged $10,000 for a placement fee.