From an Internet search, I would guess such a command does not exist.
For example, InfoWorld magazine from January 5, 1987, page 68, in a review of a mouse called Summa Mouse, says the following about its driver software:
The 1-2-3 and Wordstar menus are more complete. The Wordstar menu
[...] includes some Wordstar commands we didn't know existed and
creates others out of combination commands such as "delete word left"
However, that article is from just before WordStar 4.0 was released. ("February 1987 saw the release of WordStar 4", see http://www.wordstar.org/index.php/wordstar-history.) So it is theoretically possible that such a command was added in WordStar 4.
A command like you want does not occur in a list of WordStar 3 commands at wordstar.org (http://www.wordstar.org/index.php/wsdos-documentation/wsdos-commands/108-wordstar-3-for-dos-commands-reference; Internet Archive link to an alternative that disappeared: https://web.archive.org/web/20120919041753/http://www.wordstar.org/index.php/wordstar-emulator/support/wordstar-commands/90-wordstar-command-details-a-differences).
I could not find any list of WordStar 4 (or later) commands.
Finally, and you probably already know this, I read that WordStar 4 and up support programmable function keys, which you could perhaps use for this purpose:
Wordstar 4 is a vast improvement over [the function key mechanism of
WordStar 3.3]: It offers 40 function keys, each capable of handling up
to 30 keystrokes (we experimented -- the documentation doesn't say),
and patching them only takes a few minutes.
Source: Review of Wordstar 4 by practising psychologist (!) Bernie Zilbergeld in InfoWorld magazine from April 13, 1987, page 50, https://books.google.com/books?id=HDwEAAAAMBAJ&pg=PA50&dq=%22function+keys%22.
Finally finally, note that the same review suggests that
"Real Wordstar users don't use function keys" seems to be the theme.