Custom GTK2.CellRenderer?

I'm trying to write a manipulating version of GTK2.CellRendererText,
and for now am just trying to get a handle on the render process. This
code achieves nothing:

class LoggingCellRenderer
{
    inherit GTK2.CellRendererText;
    mixed render(mixed ... args)
    {
        write("render(%O)\n",args);
        return ::render(@args);
    }
}

int main()
{
    GTK2.setup_gtk();
    object ls=GTK2.ListStore(({"string"}));
    foreach (({"foo","bar","-- New --"}),string kwd)
ls->set_value(ls->append(),0,kwd);
    GTK2.Window(GTK2.WindowToplevel)->add(GTK2.TreeView(ls)
        ->append_column(GTK2.TreeViewColumn("Item",LoggingCellRenderer(),"text",0))
    )->show_all()->signal_connect("destroy",lambda() {exit(0);});
    return -1;
}

The write() call never happens; the overridden render() is never
called. Is there a way to hook into this sort of thing via
inheritance?

ChrisA