iExpenses - Create Expense Lines that are only approved but not Invoiced?

Hello everyone!

I have a business requirement to setup iExpenses so that a specific expense type (airfare) is to be submitted through iExpenses so that managers and AP will approve, but when invoicing (Expense Report Export), they do not want to have these lines created or possibly not invoiced to the employee.  Employees should be able to submit expense reports for any expense type, but only airfare expenses are not to be invoiced to the employee.  Basically, were will be using an outside vendor (a) to book travel, and airfare is paid for by a 2nd outside vendor (b).  That outside vendor (b) will be responsible for