I used my trusty MityVac 7201 and the side port on the transmission. I filled it with 8L of fluid and put almost all of it back in. I think it's a lot easier than trying to fill from the port on the bottom. From what I could determine, the side port is at the same level as the top of the tube on the bottom fill port.

My friend, who was a BMW Master tech, said they did it that way at the dealer, but he had left the dealer about a decade before this model came out.