What if you made a 3 sided "box" type shelf made of riged board (like foam core or plastic corregated board) and used long t-pins to mount this board to the wall then put your objects on this shelf. The shelf will be light weight enough to be mounted w/pins and sturdy enough to support your objects. Correct placement (and enough, especially all along the bottom angled in and down) should give it enough strength to support if the shelf is not too deep...perhaps not more than 4 inches....I am sure others will have ideas