Group transform; Selected object based tangential group scaling

Group transform, based on a selected group member. For example, I have a packaging die line, I want to scale one panel to a specific height, and I want the other group parts to scale up with it proportionately. Right now, what I do is: I create a rectangle shape in the size I want, lock it on the artboard, and then eyeball progressive upscales of the group over it until the panel I’m scaling lines up with the locked rectangle, and that process is madly time consuming.