[...] he's very sensitive and cargo won't be good at all for him!
We've been through this (Germany to Detroit), evaluated all options and ended up using
http://www.flypets.com/ in Frankfurt.
I dropped the cats off at Pet-Air in Frankfurt, my wife was already in the US and picked them up at the cargo terminal. Not cheap but easy, Pet-Air also took care of all the paperwork and the cats appeared less stressed then when we relocated a few years ago from Düsseldorf to Stuttgart and transported them in the car.
Cargo sounds horrible, but the crates get handled carefully, are transported separately and they provide the animals with water during the flight. Other than the transport to / from the terminal to the plane, the animals are in a quiet environment, only with the humming of the engines in the background.
If we would have transported them in the cabin (what isn't an option for your big dog anyway), they (and we) would have had to go through all the stress with security, people walking by, waiting in the loud terminal and so on.
Now, "hitchhiking" in a plane puts the stress to a whole different level - only the biggest business jets can cross the Atlantic non-stop, what means that even business jets at least have to stop in Island for fuel. Most smaller planes require multiple fuel stops, typically in England, Island, Greenland, Canada and the US. Expect at least a week in a very loud single engine plane for such a trip, plus having to deal with customs at every single stop. Bringing a dog into these countries might or might not be an issue.
All of this (assuming you can even find a pilot who is willing to take your dog, what I doubt) vs. quick 9 hours in an airliner? I'd pick the airliner and an experienced pet transport company...
