I do not know if it's possible, but can be done if the ring is set up somewhere high above the ground as players step on it do not fall down but to stay in the ring if there is an invisible floor? It might not be something invisible like blocks of BlockMaker. And create a ring with him to create the block below and do not fall for the players.
For example, if the ring is in the air, if he would fall below
http://prikachi.com/images/142/6426142c.jpg
As I entered it to retain on it!