Sorry for a long reply. Unfortunately, no — that's beyond my qmake skills, so I wasn't able to easily fix this.
pkgconfig file created on OS X misses some pathsThe original .pc file only sets Cflags to be Cflags: -I${includedir} -F${libdir}. Since Qwt installs the actual, non-Qt-style-proxy headers to qwt.framework/Headers, projects relying on pkgconfig fail to find those.
Updated slides.
Added Rudoy 2014 MSThesis.
Added C++ filtering code.