take a small piece of live rock and place the mushroom on it. Take some mesh ( bridal mesh) and wrap it around the rock and the ricodea, so that it will stay put on the rock and still get flow. After about a week it will have attached to the rock.
another way is placing it on your sand bed for about 5 days... this allows it to attach to the sand. The sandy bottom will become the base for you to super glue it to a piece of live rock... make sure you use a gel super glue.