Is it possible to set a modifier as a QShortcut?

Question

shortcut = QtWidgets.QShortcut(QtGui.QKeySequence(QtCore.Qt.Key_Shift), MayaMainWindow)
shortcut.setContext(QtCore.Qt.ApplicationShortcut)

I have a system in place for overloading Maya shortcuts, as and when needed. I want to do this with the shift key, however simply writing it as above seems to do nothing. Not even an error message.

I have tried

QtGui.QKeySequence(QtCore.Qt.Key_Shift)
QtGui.QKeySequence(QtCore.Qt.Key_Shift + QtCore.Qt.SHIFT)
QtGui.QKeySequence(QtCore.Qt.Key_Shift + QtCore.Qt.NoModifier)
QtGui.QKeySequence(QtCore.Qt.Key_Shift + QtCore.Qt.NoButton)

I want to run a custom shortcut when only the shift key is pressed.