Thanks!
Yes, see
http://jackaudio.org/api/group__ClientThreads.html
libjack offers jack_client_create_thread(), which is useful for helper
threads.
Where should our DAW call this function? From inside the jack callback,
or from outside (e.g. by the `main()` thread)?
Also, what should we pass for the "priority" argument? Probably the
result of `jack_client_real_time_priority` for the already running
realtime thread?