I did the tranny fluid change today, and at 50k miles the old fluid was pretty dark. Lifetime fluid my ass, BMW! Now the 1-2 shift seems to feel smoother (I used to have to double-clutch when cold to ensure smooth shifts) so I'm very glad I did it.
While I was under there I manually powered the pump to drain the fluid in the cooler. As another poster mentioned, I did so by slitting open the pump wire loom and scraping off the insulation on the red wire (+12V). Then I temporarily connect a battery +12V to the red wire, and connect another wire between the battery ground and the tranny case (which acts as a ground for the tranny fluid pump). I manually connect the ground wire in 15 second bursts to power the pump 3~4 times. Quite a bit more fluid were pumped out of the cooler that way...until there was just nothing more to come out of the drain hole.
As for filling the tranny, I initially filled up to the fill hole level, then I hand-tightened the old fill plug and cycled the pump for another 45~60 seconds (also in 15 second bursts). Then I think I added another ~300ml of fluid and re-installed a new fill plug that I bought (I discarded the old drain and fill plugs).
Of course, after I was all done I wrapped some high-temperature electrical tape over the pump wire that I had exposed and doubled the protection with additional wire loom just to be safe. Overall a very simple procedure--figuring out how to power the pump and cleaning up the occasional spills probably took more time than the actual procedure.
By the way, my filter mesh screen was also very clean, but since I had it out I just installed a new one that I bought along with the new crush washer.