The 27-year-old has offered support to the Hearts players during a campaign which has left them relegated from the top flight.
Prime - who practises at an independent church in Edinburgh - has been issued with a training kit and attends matches as well as making himself available to club staff during the week.
His role has been appreciated most by Locke. "He's a great lad to speak with and the players can speak to him in confidence as well," said the Hearts manager.
"Sometimes you need someone who will sit and listen and he has been there for all the boys. I had never experienced it before in my career before I went to Kilmarnock. I saw the benefits of it and Hearts brought [Prime] in. He has been a great help and if you speak to all the players they'll tell you the same."