Was your friend’s layout just in Great Model Railroads 2015? The lead story shows a layout where the gentlemen is doing just that. I did try and was happy with it until the Flyer link coupler with the metal weight tried to cross the magnet. The train froze in place… neodymium magnets are quite strong. I also would prefer to have the magnet hidden. But if you are not running Flyer link and don’t care about the magnet being on top of the ties, it all becomes much easier.
No. He wasn't in the magazine but he could be. The magnets are available in all different diameters and heights. Since you are willing to use cardboard ties, you could find slightly larger ones to use concealed. I have square ones that are close to the thickness of card stock.