The simple solution is for Cyprus to refuse them docking privileges. Then they could not go to Gaza because they came from Lebanon and not Cyprus. Since according to the Lebanese, a state of war exists between Israel and Lebanon, Israel would have the right to stop them. Even the UN would have to stop them under the resolutions passed after the last Lebanon war.
Man shot dead in northern Israel town of Bi'ina, police say the murder was gang related (Haaretz)
from the article: Lebanon to UN: Israel will suffer consequences if our ships are attacked