Aha... I see now. I haven't been in a similar situation, but I would think that it would take a special kind of submissive to help you in that task. They would have to be completely confident and self-assured in order to participate in a scene knowing that they were being watched as an 'example.' If they were to participate in a scene with the new dom, they'd have to be patient and forgiving enough to understand that he might be a little awkward or seem insensitive, while he's just learning.
My mistress has fine-tuned her skills on me, and they are always developing... but I would be a little hesitant to be topped by someone who has never done it before. I guess the sub you have with you would have to ultimately trust you more than anyone else, since you are the mentoring dom and supervising the scene.