Ticking entire threads

[Harry Putnam]

I'm a big fan of dormant ticking (using ? to mark a message)

When marked this way, you only see that message in the summary buffer
if someone replies to it.

I'd like to be able to tick `dormant' a whole thread;

I've been jumping thru the manual on such things as `i dormant <RET>'
and `Ctrl-s  tick <RET>' but not finding a way to mark an entire
thread as dormant.  The `?' does not follow the process mark (#) so
that method is out too.

Is there such a command?