How to override showPicker of SelectItem

[jjh]

I would like to override the default behavior of showPicker of an SelectItem, something like this:

@Override
public void showPicker() {
	if (someFlag)
		showCustomPicker();
	else
		super.showPicker();
}

but since the gwt-method is of course never called by the js-widget it doesn't work.
Is there some other way to do this?