Here's a thought.
Hold no hearings or votes on President Obama's nominee to the Supreme Court.
If Clinton or Sanders wins the Presidency on November 2, then on November 12, the day the Senate reconvenes, hold a voice vote to confirm Merrick, the "moderate" candidate. Guaranteed that although he is no moderate, he is more moderate than anyone Clinton or Sanders will nominate when there is no political reason to not go full lefty.
They won't, though. Republicans always play by the "rules" when they have the power, then get screwed by the Democrats when they don't.