If you retract flap all in one go, ok your can stop the sink by increasing angle of attack, yeah? Well if you are demonstrating that to a student then there's really not that much more workload involved in getting them to adjust trim on short final after lowering flap when within easy gliding distance of the runway is there? Or am I being daft here?
Do you teach big airliner style circuits too perchance?
VFE.