The current staff member that you WOULD give the "interim" tag to is one of the applicants so if you do that most decent candidates are not going to apply because it looks like you already have a coach in waiting. A lot of coaches do not want to stick their necks out looking for jobs in case it causes a problem with their current employer, Why do that if it appears the job is already spoken for.
Now I know and agree that said current staff member is a "great guy" and all that, but he is not going to get the job. Putting that interim tag on him would only make your situation worse. You certainly would not have had two of the three candidates for sure that have been seen on campus or at said eateries that are considered the "finalists".
Try to see the big picture.