pipelineJob("jobname") {
//..
    definition {
        cpsScm {
            scm {
                git {
                    //..
                    extensions {
                        relativeTargetDirectory("myRootPath") // works because implemented 
                        pathRestriction('includedPaths', 'excludedPaths') // not implemented in the dsl plugin
                    }
                    // code below doesn't allowed in sandbox mode
                    configure { node ->
                        node / 'extensions' / 'hudson.plugins.git.extensions.impl.PathRestriction' {
                            excludedRegions 'excludedPaths'
                        }
                    }
                }
            }
        }
    }
}