Play endless adverts on television for the Empire Strikes Back Hotline that casually spoil the movie for viewers (“Now you can choose whether Luke strikes back, or his father Darth Vader strikes back instead! Just call 1800-555-555 today to vote. Only 4.99 per minute, terms and conditions apply”). You can achieve this in the modern internet age of streaming and direct download by including a dozen such adverts as separate video files, and requesting the viewer sprinkle them liberally in whatever viewing playlist they use.