The only 'DIY' update method I can find is here-
http://www.bmw.com/com/en/owners/nav...gion=&country=
but this appears to be just for updating Bluetooth connectivity for new phones etc.
I get my car back on Thursday and will check the map version then. I take your point about the time the download would take, but I honestly never noticed when mine was updated. I was just aware, sometime later, that it had been.