A work-around is to tell system events to press the keystroke combination currently assigned to Format > Highlight.
Suggestion: when I write annotation scripts I capture the original URL for a document (e.g., the site from which the PDF was printed to DTPO) and then display that URL in the annotation document. This makes up for the lost URL that happens when you insert the annotation document URL into the URL field of the annotated document, and gives the reader a clickable link to the source site.