No-one's suggesting maintaining max continuous power until you suddenly chop the power. That would be stupid, and completely unnecessary for practicing a glide approach. Even if you habitually cruise at such a high power setting, do you not start making progressive small power reductions as you near your destination to prevent shock-cooling as you descend and / or decelerate? If I'm intending a glide approach I will have already gently slowed to the appropriate speed and descended from cruise altitude. At that point I'm using something like 35% power, tops, whether I'm in a Cub, an Archer, or a Yak. I don't know anyone who makes a habit of driving round the circuit at max cruise or full power, whether they are planning a powered or a glide approach.