Styling the MainWindow dock separator

Dear all,
I made a simple application with some Dock widgets inside a mainwindow.
I use, as a base style, the plastique one.
I would like to change the separator widget between the docks, but I cannot understand well
what kind of widgets are used in the mainwindow classes.
I suppose that normal QSplitter was used, but I realize that the widgets showed is not classical qsplitter (using style sheet to change, for instance, the handle, doesn't work).
I see that every QT Style has a different style for the separato.
How I can change the handle (and hence the style) of this separator ?

I would like to use the style sheet, but I think that is not currently possible, so I think that I have to redefine the style of some control.

Best,

Angelo

Perhaps QStyle::drawPrimitive(QStyle::PE_IndicatorDockWidgetResizeHandle)?