You can add a temporary user to the database for the driver. If you decide to hire him, then you can complete the set up of the user to be an employee of your company and keep tracking Duty Status Logs under the same user. If not, you can always make the user historical. I would recommend annotating the logs in the latter case.
Another way to go about it is driving the vehicle without a driver assigned to it, and annotate all the unidentified driver logs created during the test drive. If the driver is hired, then you can create a user for him and re-assign all those logs to him. If the driver is not hired, then the logs will stay under unidentified driver but they will be properly annotated explaining the situation.
Please let us know if you have any other questions.