I don't know anything about index, you could hack a bit by using Keywords
class="[=KEYWORDS]"
If you really need the index, I think you should use xslt version with position() see http://www.dnnhero.com/Premium/Tutorial/tabid/259/ArticleID/12/Beginning-XSLT-with-DDRMenu-for-DotNetNuke-Part-2.aspx