There is actually a discussion on Google Groups if it makes sense to add support for the Job DSL plugin directly into the Promoted Builds Plugin:
https://groups.google.com/d/msgid/jenkinsci-dev/e6946a1a-a207-4bc4-8fc2-b42021b996f3%40googlegroups.com?utm_medium=email&utm_source=footer

I created already a Job DSL Extension in a separate Repository (https://github.com/codecentric/job-dsl-promotions-plugin). The question is now if I should invest the time to create a PR for the Promoted Builds Plugin. The main point is here, that the extension is mainly written in Groovy. Is it ok for you to see Groovy in your code base?

Regards
Dennis