I'll disagree on this one. It's pretty simple. I have the extended seat post on my Brompton, as well as the B&W case. I've flown a number of times. Yes, I remove the seat so that it fits better, and yes I also remove the seat post.

After I remove the seat, I just drop the seat post out of the bottom, wrap it up, and put it in the case. I fold down the bike as usual and use velcro straps so that it holds its folded configuration. When I arrive, I just lay the bike on its side and reinsert the post from the bottom, and re-attach the seat. This only adds a few minutes on packing up or setting up, and requires no special tools... so I'm not sure how much simpler it can get. I think it takes longer for me to unpack my clothes and figure out where I'm actually going to ride to.

I've packed my wife's Brompton too and she has the regular length seat post. It seems to fit fine.