restrictive subset of markdown?

I have a Shiny app that users can partially 'configure' via their own config files. In one instance, I'd like to allow them to specify Markdown-compliant text, but only HTML-render specific parts of that Markdown. In particular, I'd like to enable only HTML links, but disable other Markdown elements. I see that the markdown package has markdownHTMLOptions, which seems to get partially-the-way there ... but I can't, e.g., see an easy method for say, suppressing bulleted lists while supporting hyperlinks.

Anyone know if there's a pre-packaged mechanism to effectively disable everything then selectively turn each Markdown feature back on?