My car has the battery on the motor compartment and I simply disconnect the ground. I can reached it from under the car because the cable is hanging.
I tried that emergency procedure after reading a thread here but not working. I'll keep trying.
Again , I'll also try to find a hot connection from the battery, maybe the starter, and connect positive there and ground on the hanging cable.
Thanks Roberto. I also thought of that. Something was missing there and I couldn't get it right after a 8 hours flight.
I'll keep trying, thanks for the help.