The RAF targeted the Blohm & Voss BV 238 because it was concerned Hitler would use the giant flying boat to escape.
https://en.wikipedia.org/wiki/Blohm_&_Voss_BV_238#Destruction
So, prior to April 20, 1945, Hitler, Braun, The Gobbels family, and other choice Nazis get to Schaalsee where the Blohm & Voss BV 238 is waiting.
With an overall lightened load, plus fuel tanks loaded inside the cargo bay (like these B-29s below), a range of over 8,000 km is possible.
First flight is to Fascist Spain's Canary islands for refuel. Then, it's 9,590 kms from Canary Islands to the Nazi lair at Nahuel Huapi Lake, near Carlos de Bariloche, Argentina.
http://gizmodo.com/5860250/hitlers-secret-argentine-sanctuary-is-for-sale
So, we'll need find some discrete sympathizers to refuel somewhere on the Brazilian coast. Unless a Milchcow submarine is available
http://www.feldgrau.net/forum/viewtopic.php?t=35242 But now we're involving too many people who may talk after the war.