I just ended up trying this: s6-setlock -t 200 -r ...
it'll fail with EBADF: s6lockd-helper: fatal: unable to lock /tmp/lock: Bad file descriptor s6-setlock: fatal: unable to read ack from helper: Broken pipe as the helper doesn't include an equivalent fix to 73638ee8e3c7 bugfix: setlock -r: -- Alex Kiernan