Narrowing same buffer to different regions in two windows

[Roy Smith]

I've got a file with two large sections of very similar text that I
want to examine and compare (it's C++, and a previous author did a
"cut, paste, and modify" job instead of refactoring).  What I'd like
to do is split the screen into two windows, and do narrow-to-region in
each window, ending up with each window looking at a distinct section
of the file.

The problem is, narrowing works per-buffer, not per-window.  Is there
anyway to do what I want?