The anti-static bags vid cards of motherboards come in could work. depending on your setup, they can just sit vertically above the MB, assuming you are using PCIx extenders. I built some wood rigs that keep the cards about 43 - 4' above the MB. I've seen other use shelve systems where the cards are held up by the shef above the MB using simple zip ties too.
the 'pictures of your mining rigs' threads has all kinds of different ideas...some better than others.