You could work with transpanecy in Global Mapper and "join" two map to have one with a permanent overlay.
For Android there are some programs that allow the use of your own overlays and 3D functions.
Guess the biggest problem is the fact that the gouvernment here does not care about providing proper maps for the public.
The that are available are hard to get for noobs and in most cases not good enough in terms of details and up to date infos.
A shame really that Nearmap got so greedy.