As far as I understand qmake should take care of it automatically right? It generates a makefile for dummyimplugin3 makefile.debug which has .moc\moc_dummyinputmethod3.cpp listed under SOURCES and .obj\moc_dummyinputmethod3.obj listed under OBJECTS
From the compiler output it seems it gets built and linked?:
The above problem has been "autoresolved" with a reboot of my PC.
Another problem arised: "LINK : fatal error LNK1104: cannot open file 'qtmaind.lib'"
This is due to the fact that release libraries and debug libraries are stored into 2 different folders.
So I've taken the source files of Qt4.8.4 from OSG and recompiled them with the desidered options.
Now everything works.