Couple of things my dad has done in the past.....
A friend of his was moving and hiring movers. The night before he called her up and said there was a truck drivers strike going on and that there would be no one to drive the truck. He said she can have the truck, but would have to have someone licensed to drive it. This joke could only work if he's moving anytime soon.
Another thing my dad did to someone....a group of colleagues often went in on combined lottery tickets every week. When my dad bought the tickets, he somehow managed to get an extra 10 inches or so of the lottery paper they use. He used the old dot matrix printer (this was MANY years ago) and created a 'winning' ticket that night after the numbers were drawn. The next day at work, one of the guys asked if he had checked the lottery numbers yet. My dad said 'oh no, i haven't had time...why don't you do it' and handed him the fake ticket. The guy went ballistic with excitement. I don't know how long they let him believe it......
Just a couple things that might spark some ideas for you.