ZK - Open Source Ajax Java Framework

I have a listbox with drag and drop enabled to the list tiems... when I would like to darg and drop a listitem outside the view of listbox, the scrollbar does not automatically scroll.... is there any way to make auto scrolling when you want to drag and drop a listIem??... here is my code

<zk>
<hbox>
<listbox id="left" height="150px" width="200px" onDrop="move(event.dragged)" droppable="true"
oddRowSclass="non-odd">
<listitem draggable="true" droppable="true" onDrop="move(event.dragged)">
<listcell label="ZK Forge" />
</listitem>
<listitem draggable="true" droppable="true" onDrop="move(event.dragged)">
<listcell label="ZK Mobile" />
</listitem>
<listitem draggable="true" droppable="true" onDrop="move(event.dragged)">
<listcell label="ZK GWT" />
</listitem>
<listitem draggable="true" droppable="true" onDrop="move(event.dragged)">
<listcell label="ZK JSF" />
</listitem>
<listitem draggable="true" droppable="true" onDrop="move(event.dragged)">
<listcell label="ZK JSP" />
</listitem>
<listitem draggable="true" droppable="true" onDrop="move(event.dragged)">
<listcell label="ZK Spring" />
</listitem>
<listitem draggable="true" droppable="true" onDrop="move(event.dragged)">
<listcell label="ZK" />
</listitem>
<listitem draggable="true" droppable="true" onDrop="move(event.dragged)">
<listcell label="ZK Studio" />
</listitem>
<listitem draggable="true" droppable="true" onDrop="move(event.dragged)">
<listcell label="ZK Jquery" />
</listitem>
<listitem draggable="true" droppable="true" onDrop="move(event.dragged)">
<listcell label="ZK JS" />
</listitem>
</listbox>
<separator />

</hbox>
<zscript>
void move(Component dragged) {
if (self instanceof Listitem) {
self.parent.insertBefore(dragged, self.getNextSibling());
} else {
self.appendChild(dragged);
}
}

</zscript>
</zk>