There aren’t any official solutions to you dilemmas.
For PCIe slots, one person did mount a card (a GPU in their case) above the PCIE area using DIN rails;
For U.2 drives, people have made a few versions of the 45HL SSD bracket that mounts to the inside backplate, but that can conflict with CPU tower coolers. There are any number of other 3D print examples floating around of cages to hold 15 mm drives that you could put along side the one for smaller 2.5" drives. I think Icy Dock makes some U.2 versions of their cages with backplanes. You just want to be sure you orient things so there’s still enough front-to-back airflow where it needs to go.