That is mostly bull crap. The floor of an electric oven with an exposed bake element is the coolest part of the oven. Putting foil under the bake element, AS LONG AS IT DOES NOT TOUCH THE ELEMENT AND YOU KEEP IT CLEAR OF THE AREA OF THE ELECTRICAL CONNECTION, does not hurt the element. Whirlpool sold heavy foil for the floors of their not-so-continuously-cleaning electric ovens. Manufacturers are writing manuals that, as you said, cover the entire line of ranges, both with and without concealed bake elements. The manuals are not only written for the stupidest consumer, but also for those who are barely able to understand English so they say don't use foil.
If you are still afraid to use foil, you can use a large aluminum cookie sheet, the kind with one upturned edge or lip and slide it under the center of the bake element, making sure that the door closes properly and that the back-most edge does not touch the bake element terminals. It's not foil. It's not gonna fuse to anything and it will protect a certain area of the oven floor.