As per the post title the idea is not original but I thought I'd rather do it this way. I decided to do both sides, not only for symmetry but to halve the weight load of each hook. I took 2 clear medium Command hooks and sawed off the tops with a carbide rod blade so that the entire hook would fit within the flat part of the hatch molding. Filed the cut ends smooth then painted them matte black. Used two adhesive strips per hook to cover the entire hook back, then trimmed the excess off with a blade and blackened the white adhesive cut edge with a marker pen. Not wanting to give the car holes that it was not born with, I used binder clips for the shelf attachment. The shoe lace is a round heavy type used with boots. I sewed a loop on one arm of the clip and finessed it with 1/4" heat shrink tubing. Holding the shelf at the desired elevation/angle, I stretched the shoelace to the hatch molding keeping the lace at right angles to the shelf surface. This gave me my mounting point for the hooks. Working from the inside with the hatch closed, I formed the upper loop on the hook with the desired amount of slack and temporarily fixed it with a clip. Since the lower attachment is removable, further work on the shoelace can be done away from the car - in your significant other's sewing room or whatever. Just be sure you slip on the second heat shrink tubing before sewing the loop permanently. Shrink the second tubing in place and the only thing left to do is hook everything up. Attached are pictures.