Superscript formatting of text in custom metadata field for Chapter Heading subtitles

My book has Chapter Headings with subtitles. I include the date the chapter takes place in the subtitle. In order to do this I have created a custom metadata field called “subtitle” for all of the “Chapter Heading” section types. See image below for what this looks like in Scrivener.
Scrivener view.png

However, when I compile the document I have no way to indicate that the “th” in 19th should be in superscript font. Here’s what the compiled version looks like.

Any suggestions on how to tackle this? I assume I could make the edits after exporting from Scrivener but that would be a decent amount of manual work.