Bug 157072 [ActionSets][Contributions] QuickMenuAction funtionality should be made public
The QuickMenuAction class should be made public and usable by IWorkbenchWindowPulldownDelegate{2}. As it is you need to roll this functionality yourself in the run method of your delegate (and it is by no means straightforward).
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/ide/actions/QuickMenuAction.java
* 
     * @return a widget relative position of the menu to pop up or
     *  <code>null</code> if now position inside the widget can
     *  be computed
     */
    protected Point computeMenuLocation(StyledText text) {
        Point result = text.getLocationAtOffset(text.getCaretOffset());
        result.y += text.getLineHeight();
        if (!text.getClientArea().contains(result)) {
			return null;
		}
        return result;
    }
    /**
     * Hook to compute the menu location if the focus widget is
     * a tree widget.
     * 
     * @param tree the tree widget that has the focus
     * 
     * @return a widget relative position of the menu to pop up or
     *  <code>null</code> if now position inside the widget can
     *  be computed
     */
    protected Point computeMenuLocation(Tree tree) {
        TreeItem[] items = tree.getSelection();
        Rectangle clientArea = tree.getClientArea();
        switch (items.length) {
        case 0:
            return null;
        case 1: