Now at 1.598, the functionality suddenly appears in every job. I was configuring a new job from scratch, and there it was, right above the "Build" section. Seems to work fine. I installed it again on the old system, and it started working right away there, too.
Speculating, maybe something in the system config.xml blocked it from appearing, but creating the new job tickled the XML in some way to make it finally appear? Or some other fix between 1.585 and 1.598 cleared the blocking bug?
I think I'm more upset that nobody commented on this or on the thread or two I posted on the Google group, and I still think the feature could use better documentation.
As a suggestion, if there is a set of steps to follow to ensure that the functionality does appear, or a simple checklist of items that need to be configured before or after installation, it would help to place that on the plugin's web page.