[NTG-context] Appendix Page Numbering

I use \definestructureconversionset [frontpart:pagenumber][][romannumerals] to make sure the numbering of my pages in frontmatter use Roman numerals. Not only are the pages numbered with Roman numerals, but the PDF index links and PDF page numbers use this as well. I would like to do something similar for the backmatter, but I would like both the page numbers and the PDF index links and PDF page numbers look like A1, A2, ... (for appendix). How can this be done? Thanks, Troy Henderson