This idea my not be a good workaround for you, but I wanted to offer it in case it is helpful to you or others. 

If you are using a Google/Gmail based email system, you can use an alias with the "+" character, see https://support.google.com/mail/answer/12096?hl=en I am assuming that other email provider services may also support the same, but to what degree and which ones might support this I don't really know. This has been invaluable to me in testing.

There is also the divertemailto setting available to config.php:

// Divert all outgoing emails to this address to test and debug emailing features
// $CFG->divertallemailsto = 'root@localhost.local'; // NOT FOR PRODUCTION SERVERS!

The divertallemailsto feature has also been invaluable to me in testing.

So those don't deal with your specific question, but perhaps that helps as a workaround.

Jamie