How to subscribe to PR updates that are not assigned to a maillist?

[Anonymous]

I want to receive updates to a few PRs that are submitted by someone
else. When such PR is assigned to a maillist (e.g. freebsd-ports-bugs@)
I can subscribe to it and filter messages based on PR number. But what
I'm supposed to do when it's assigned to a person with @FreeBSD.org
address?

Is querying CGI interface the only option? For example, in bugzilla I
can add myself to CC list.