When I get the small (under 1.5") clams I use a drop or 2 of Krazy Glue on one side of the shell to attach it to a piece rock. This has worked well at placing clams amoung the live rock crevices in my tank and protecting them from getting knocked around by crabs and snails.
Oyster Feast is a great food, I don't know how well it is for small clams, you might consider feeding a phyto plankton food as well.
Update: clam attached to the price if rock rubble Thai I buried underneath the sand. I moved it up a little less than halfway. Just moved it and its closed up. Do y'all know if the clam can detach itself if unhappy or something?
I would move it back to the sand and leave it be. It's a little Maxima and they hate to be moved around too much. I'd move it to where it was happy and leave it there for a few weeks.