For our purposes, we set up an entire group for non-employees so that they were completely separate for reporting. They are under the same policy, but we wanted the option to change the rules for non-employees. For example, we require non-employees to submit receipts with every item. For employees, if they have a corporate credit card and the item is less than a certain amount, no receipt is required.
You can ask that the non-employee option in the setup in Concur can be added. There you can classify the user as a contractor. If they wind up getting hired on full time, you can reclassify them as an employee. The only thing is there is a start and end date for the contactor account that you must include. Sometimes there is no known end date for contractors. My work around is I actually create a bogus employee id # when creating an account for a contractor and fill out the rest of the fields as a regular employee. Not as clean, but it works.