Position a whiteboard towards the rear of the room to record items that it is not appropriate to deal with at the time they are raised. By recording them for all to see the participant can feel confident that a genuine concern will be dealt with rather than just glossed over. By having the board at the rear of the room in the line of sight of the trainer, but out of direct view of the participants, it acts as a prompt for the trainer.
Once the matter has been covered seek approval of the whole group (not just the person who raised it) to remove it from the list.