ListCtrl drop indicator visual feedback

Just added an item to the wiki, a mixin to auto-scroll a ListCtrl in
Report mode when it's being used as a drop target:

http://wiki.wxpython.org/ListCtrlWithAutoScrolling

On a related note, does anyone know how to provide visual feedback as
to where the item will be inserted? I'm imagining a heavy horizontal
black line in between two list items showing where the dropped items
will be inserted.

With the following code in the OnDragOver handler

        rect = self.dv.GetItemRect(index)
        dc = wx.ClientDC(self.dv)
        dc.SetPen(wx.Pen(wx.WHITE, 1, wx.DOT))
        dc.SetBrush(wx.TRANSPARENT_BRUSH)
        dc.SetLogicalFunction(wx.XOR)
        dc.DrawLine(0, rect.y, rect.width, rect.y)

I could get an XOR'd line to show up on Windows but it does nothing on GTK.

I'm new with graphics context stuff, so perhaps drawing during the
handler is not allowed. Does anyone have any ideas or code they can
point me to? Would you have to go to a full owner-drawn list for this
effect?

Thanks,

Rob