I don't remember how I did it. One one phone the internal storage was almost full, so the installer offered me automatically to install to SD, so I just had to tap onto 'OK'. So just fill up your internal with a huge folder until only a couple 100MBs are free, install Navigon (to SD when asked), delete the temp. crap folder with scrap files .

Result: on SD card: /Android/data/com.navigon etc (NOT /Navigon/..) !!