Currently the Jenkins Next Build Number plugin permits one to set the value for the next $BUILD_NUMBER through user interaction (it is an action). For Job DSL users, the natural place to set job configuration details would be through the DSL.

Proposing extending the DSL as follows:

freeStyleJob(String name) {
  name(String name)
  nextBuildNumber(int nextBuildNumber)  // This is new
  // etc...
}

Values lower than the currently pending build number will be ignored. Values less than 1 will raise a DSL validation error.