it's all about keeping them in a cool, dry place with airflow. There are a gazillion studies on what inhibits or encourages sprouting (everything from essential oils to keeping them near or far from apples, due to the ethylene). Bottom-line is it seems no one really knows with potatoes, and dioscorea yams, while a close cousin, are even less well understood.
But cool, dry, and with airflow are what helped me keep my dioscorea from sprouting for 6 or so months.