Although i didnt use the NCP3063 (yet) i can show you how to stop your oscilator .http://www.mastercity.ru/old_forum_archive/2/203532.shtml
In the second picture of this link you can see how they create a feedback on the IR2153 .
This *trick* is usable with a lot of pwm generators .
You can stop the sg3525 with the shutdown pin .
But unofficially you can stop the oscilator just as effective by pulling the inverting input below its workrange .
I assume that with the NCP3063 pulling pin 3 to zero will also stop the oscilator immediate .
Since this chip has current sensing you can also pull the current sense pin above 1 volt .
All of these methods will stop the pwm