A novel device is provided for the treatment or prevention of a disorder of a patient characterized by regaining lost weight after RNY surgery as a result of dilation failure of the gastro-jujunal stoma. One embodiment the device involves inserting an envelope-like device into the patient's body during or post RNY surgery. Once inserted, the surgeon positions the device to substantially surround the RNY pouch. The device automatically applies a localized compressive force against the proximal Roux limb (jujunum), proportional to the degree of over--fullness of the Roux pouch. Thus a sphincter-like replacement for the pyloric valve is created that substantially reduces the efferent flow of chyme through the g-j stoma, thereby substantially preventing traumatic dilating pressure forces from being imposed on the g-j stoma. The present invention thus uniquely provides a safe and reliable means to ensure the long-term success of the RNY procedure.