From starwars.com:

Lambert had already been thinking of building a Darth Vader hot air balloon when FanWars leader Nicolas Lelong (TK-2054) first brought up the idea. “For me, it was more of a joke and a fantasy, but Nicolas took it seriously and found the idea wonderful,” Lambert says. “He made contact with Lucasfilm in order to try to get their agreement.”

I’d love to see this in person. What’s really cool is that the sound the fire makes sounds just like Vader breathing.

Link