This one worked better than my wife and I could have ever expected.
It was back when magazines had those little cut out coupons that you filled out and sent away for more information. They're not very common nowadays, but with a bit of cunning you might still be able to make it work.
What we did to get revenge on someone who thought he'd stitched me up, was to fill out every single one of those little information request coupon things, with his details and send them away.
After about 6 months of pretty dedicated revenge, he had mail arriving from all corners of the globe offering all sorts of things, including how to build a ship in a bottle, forms to fill out to become a Jehovah Witness, after all, he'd sent a request for it. How to marry an Asian bride. All sorts of sex toy literature, university courses, learn a new language, house plans, sewing patterns, colouring in competitions, you name it, he received it.
His girlfriend was getting really worried that he was lying to her and leading some sort of double life.
He never suspected it was us and when we finally told him, he still didn't believe us.
It was awesome.
We got a lot of the magazines for free from doctor waiting rooms, hairdressers, friends etc and the coupons could be sent free as well. So it didn't cost much either.
I'm not sure how you would adapt it to make it work today, but if you can make it work, you'll get sweet revenge.