I understand the question.... I just don't understand why its a question.
Are you asking how can you QT him and feed him live fish? Because at that point he isn't in QT because their is another fish?
If that's the question. I think you are misunderstanding QT. We QT fish to insure that they don't have anything fatal so that it doesn't make it to our display tanks and spread. That being said you don't have to QT fish one at a time at least IMO ive QTd a few fish at a time multiple times.