Of course, once I posted the above it dawned on me that the main purpose of `qmake` is to build standard makefiles, so instead of going through a .vcproj conversion, the better workaround might be to create a project by importing the makefile that qmake produces (particularly for non-Windows platforms).
I haven't tried this (I'm not working with Qt stuff at the moment), so I don't know if there are roadblocks that would prevent this from working well.