I mean, really, it already uses 3 out of 4 as polearm animations, and it's possible to only use 2h wpf? And a lot of the smaller 2hs (considering all other 2hs are smaller) have it.
Leave all the animations same, just two modes for 2h/pole.
Or if you are really great you can make it use both WPF without interfering with secondary modes (it's only possible with WSE as I can remember).
I think it's already underused atm, so it would buff it a bit.
UP: also Great Long Bardiche has better stats then Flamberge and is almost half as cheap, so it won't really impact pole balance