Actually the binary built can be installed in a private path alongside qtnetwork (in it's package) and might even be a private lib without headers. That should be enough to keep stuff in sync.
By the way, how is mumble's porting to qt5 going?
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Lisandro Damián Nicanor Pérez Meyer
http://perezmeyer.com.ar/
http://perezmeyer.blogspot.com/