Thanks to all who contributed. Not sure if I am anything wiser. In a similar situation, my instinct says that I would still think twice about dumping fuel overhead Berlin. Some of the aromatic hydrocarbons found in fuel have such strong bonds (such as benzene) that they are indistructable and will end up landing somewhere. The term 'vaporizing' is a little misleading, because it seems to suggest that the fuel will be broken down and simply dissapppear.
Tough decision, altogether.