There must have been some unstated reason (inter-company politics most likely) they didn't talk to either Imperial Airways, who had the fully surveyed Kangaroo Route from London to Australia for the Empire Class flying boats, or KNILM, who had had a fully surveyed route from the Netherlands to Java before the Germans invaded, and who were still operating in the Dutch East Indies. They couldn't have used the original Med segments, but IIRC by that time the Kangaroo Route had been diverted to fly via Freetown in Sierra Leone to Khartoum, and Freetown is about the closest point in Africa to Brazil.