Do you have a family member going under anesthetic for a medical procedure anytime soon? If so, I think you should try this, and, in fact, I will spot you the money to do so.
When this person wakes up from the anesthetic, have a nurse say, "My god, it's a miracle," and run out of the room.
Then have a doctor (or someone pretending to be a doctor) come in the room and say something like, "Karen... it's... it's so good to have you back. My name is Dr. Roberts. Karen, do you remember why you came to the hospital originally?"
She'll say it was to get her appendix out, or whatever.
"Yes. Yes, good. It seems your memory is still intact. Karen, I don't know how to say this, but there was an issue with your surgery and you slipped into a coma. You've been asleep for 25 years."
"We've notified your family." He points to a dusty stack of presents in the corner. "They never forgot you, they would bring you a gift every year on your birthday and they'd throw such a fit if we tried to move them. They had faith this day would come."
There's a knock on the door and you and another member of the family come in wearing full old-age prosthetics. Ideally you have some 30-year-old playing your friend's grown-up five-year-old kid.
Just cry a lot and at some point ask your friend if she wants to see what she looks like now. Reluctantly hold up a hand-mirror to her face which you've pasted a picture of the Crypt Keeper or Zelda Rubinstein or something to.
This isn't a magic trick, of course. I guess it's a practical joke. But really, I'd like it to be more than that. I'd like it to be something people do even if the target knows what's coming. This may be ambitious for something so complicated to pull off, but I'd like it to become a fad that sweeps the nation. Like planking or Tebow'ing once were. VanWinkl'ing.