The only egg diagram I'm familiar with shows the effect of gravity on wing loading and speed on radius. You may be thinking of the reduced radius you can get after slowing down from climbing compared to the circle drawn by a sustained rate flat turn. You can illustrate that with AH film by turning trails on and taking a couple of screenshots. That could look like the top half of an egg. If you teach this as a high yoyo you might make sure he understands the basics of turning, i.e. speed, G load and drag, before you teach ACM.