The answer, as I eventually worked out is incredibly simple. If the holder/power socket is turned 90 degrees it will go on horizontally allowing the garmin to be mounted in portrait mode. Set the Sat Nav to portrait mode and all is good!
When i picked up my new 950S last month, the mechanic at the dealer did exactly that, witch resulted in a Zumo 396 mounted in portraid mode, while not supporting that.
15 minutes later all was well, all they had to do was drill a hole in the mount to accommodatie the 396 connector.
Apart from that, the cradle for the 396 and 595 are basically the same.
Nice when everything turns out well.