On installing, it appeared the plug-in did not work as advertised - I could only find a 'build now' link when following the 'promotion status' link which appeared on the project after adding a promotion to its configuration.

Using that created a build which never completed, and could not be halted. Checking the logs, there was a NPE, and it looks like bug #JENKINS-22068. This creates the impression that the plug-in is broken.

Further research finds that although there is a bug, my problem is simply that the build needs to be run again having added the promotion:

http://stackoverflow.com/questions/20960783/jenkins-promoted-builds-promotion-ui-missing

Please mention this prominently on the plug-in's wiki page here, it will help other people like me!