erp5_upgrader can be used to upgrade any site:

 * create Business Template which overrides upgrader scripts in its own skin (XXX_erp5_upgrader)
 * set extremely high business_template_skin_layer_priority (like 10000.0)
 * develop this Business Template
 * to upgrade site install first XXX_erp5_upgrader, then erp5_upgrader
 * voilà - site upgraded