IExpense only with HR Employees and not as defined User?

Has anyone implemented IExpense without setting up Users accounts?   So we will be setting up employees and using delegations to enter expense reports for others.  We have a large user base that does not have email or Miscrosoft Active directory (AD) accounts, so we do not want to set them up in AD and then in UMX or FND User (Define Users).

Plus - less cost

Minus -

   Notifications - go to Sysdmin and preparer

   Audit - employee never sees accounts or reimbursements reconciliation

thanks,

Phil