I just found https://answers.atlassian.com/questions/48062/create-task-at-a-particular-workflow-transition which appears to answer this question.
[Didn't show up in my earlier searches, but came up in the Related Questions sidebar]
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
We're bringing product updates and pro tips on teamwork to ten cities around the world.Save your spot