You can use QMSEDX without a publisher, that's no problem at all. However you're still correct that the trigger for your task has to be changed to "by an external event" and no other triggers (for example "on a schedule") can be added.
But that shouldn't be much of a problem since a trigger "on an external event'" can be fired by anyone who feels like it. For example, by a dummy document that is reloaded on schedule, and as only activitiy performs an EXECUTE of QMSEDX. Or by Windiws Task Scheduler.