I've seen over-the-shoulder type sheaths that kind of rotate while you pull... I can't really imagine the line the sword takes which doesn't include going through my shoulder, but that doesn't mean that it doesn't actually work. I tend to agree with Oni though, that you would store it kind of like a polearm, and if you plan to use it, you have it unsteathed.
On a side note, flamberge can and does refer to multiple things. Sometimes, it simply means any sword with a wavy-edge, and sometimes it refers to a huge cavalry monster. IME, it usually means the second one.
-nameless