It is safe to assume that most Arabs in Gaza would like to live a normal life and be rid of Hamas, but they still believe in the Hamas cause and will not do anything to actively stop them from firing rockets near their homes, here is my solution which would most probably have a big effect:
Israel should setup Iron Dome batteries inside gaza or right near the gaza border, as soon as it detects a rocket launch let them knock it down over gaza, if this keeps happening the Gazans will know that each time a rocket is sent up it will just rain down in pieces over their heads, it would make it almost pointless to support shooting rockets, the Gazans will make them stop it.