So you like the ghost flame idea huh? How about this -
Get some light ghost stripes that start really low in the front, and as they move up the front of the car, they turn to a flame. They would be really light, and only show up in certain light, just like you stated. As they move up the hood, they would look like they a blazing. There is a car that was featured in 5.0 mag that had a ghost flame job on it that was hard to notice until the sun light hit it just right. It was a '99 Cobra with a Saleen body kit on it. It was the cover car. If anyone has the mag, can you scan the pics. I don't had a scanner on else I would.