Bunch of amateur stackers in this thread - as an expert, let me weigh in (pun intended).
The way that others have gotten key imprints on their screens is by stacking things on the center of the closed-lid computer, causing inward bowing of the lid. You can get away with light items this way (glasses, phone) but anything heavier and you'll be pressing the screen against the keyboard and getting key imprints on it.
The right way to stack is by distributing the weight uniformly across the lid of the computer, including its structural edges. For example, if the first item you place on top of the closed-lid computer is a book that is larger than the computer, it will spread the weight of anything stacked on top of that evenly including across the much stronger structural edges of the computer.
That does seem to stack up.
I salute your spirit, though that worries me...I have a special "stacking tray" that is simply a flat tray that is larger than my 14" MacBook Pro. Everything I want to stack on top of the computer, I put on that tray and it distributes the weight evenly. I have stacked books, moving boxes, car parts, air conditioners, anything that I wanted to stack on top of my computer I have been able to stack using this method. I even had a bet with my friends that I could stand on top of my computer with my full weight using this method and not cause any damage to it. Whether I won the bet or not isn't important, what's important is that we can stack to our heart's content and if the computer breaks or is damaged, at least we lived and did all of the stacking that we wanted to do.