The plug & socket used by BMW is smaller than the conventional car accessory unit - its called a DIN Plug.
Plugs are available from the usual sources (Motorworks, Moto-bins etc) or a cheaper version is available from Vehicle Wiring products here:
http://www.vehicle-wiring-products.eu/VWP-onlinestore/switches/12vacc.php
The BMW ones are better quality.
You can also get a plug that fits both the DIN and car sockets - it has a removable sleeve through which to adjust the diameter.
All are easy to wire up. I have such a plug on my battery charger for use on three BMWs. None have CANBUS fortunately as that will usually require a direct connection to the battery. You'll be OK with the 1150 as it doesn't have CANBUS either.
Bob.