Most nations agree Israel's "settlements" in the occupied territories are illegal. Even Israel's strongest supporters (like the United States) clearly oppose and condemn new settlements.
At the same time, the US provides billions of dollars annually in aid to Israel.
The US should inform Israel that every for every new settlement family it approves, we will reduce the annual aid we supply them by some amount (perhaps $1 million).
Put the ball in Israel's court. Make it so that if Israel chooses to approve new settlements, in doing so it broadcasts to the world that it is knowingly giving up tangible external support. And make it so Israeli leadership is accountable to its voters for giving up the foreign aid it receives.
In short, stop making new settlements an easy choice.