I agree with Jared's opinion that you should either not use them at all (as they are potentially confusing for all users) or you should do nothing special for screen readers at all.
@jnurthen since my website is about royalty I use Roman numerals if the regnal name needs it (George VII for example). So I think in my case there would be no confusion for anyone, sighted or not.
@jnurthen It was me to do about not irritating users when the text is being read. But since it is clear from the context of the page and site what is meant, I think I indeed might be safe by doing nothing special for screen readers.