This seems to be more of a Swordsage discipline than anything else. And I think(hope) that was the creator's intention:
Quote Originally Posted by JoshuaZ View Post
All Narrow Bridge maneuvers are supernatural unless stated otherwise.
I don't know about you, but I was pretty sure swordsages were the only ones who normally get supernatural maneuvers.

Although I would really just allow it to be swapped for any discipline the same way most of the homebrew disciplines are. Because, as the OP mentioned earlier, the discipline is very circumstantial and spreading out maneuver choices over different disciplines makes your character severely weaker.