there have been some threads about this topic in the very past. Maybe there is some current information around...
Sometimes we have to restart our application servers due to some change in the appserver-configuration (via blasadmin). But as users are normally working with BL (yes, that's what they should do ;-) ) there is no chance to get a "job free" environment other than phoning around and tell them to stop it for a while.
If there's still no such possibility did someone open a feature request and could post the ticket number (or better QM-ID) so we could attach to this?
You can do a soft shutdown of the appserver, that will wait for jobs to finish and not take new jobs.
What would be ideal for this kind of situation is to be able to pause the running jobs, restart the appserver and have it resume execution..which would be a good rfe ☺