In SVN trunk ( = 5.2 development branch ) you find a draft of a QwtPlotHistogram implementation. It's still incomplete, but might be enough for your needs. Here you can overload QwtPlotHistogram::drawColumn or implement tooltips easily using QwtPlotHistogram::columnRect.
At the moment my focus is on the 5.1 release and the 5.2 branch is a bit orphaned. So it might need some time until a 5.2 release, but you can copy the implementation to your code and backport it to 5.0.
Uwe
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