groovy:
import com.pmease.quickbuild.*

def srcConf = system.configurationManager.get("path/to/src/configuration")
def srcBuild = srcConf.getLatestRecommended()

Context.push(srcBuild)
try {
  def promotion = srcConf.findPromotion("nameOfPromotion")
  promotion = system.scriptEngine.installInterpolator(promotion)
  promotion.promote(srcBuild, [:]) // the second param is an empty map, you may pass variable name to value map if desired.
} finally {
  Context.pop();
}