code: public static void addCustomToLaunch(Properties ltiProps, Properties custom) 
  	{
          Enumeration<?> e = custom.propertyNames();
          while (e.hasMoreElements()) {
              String keyStr = (String) e.nextElement();
              String value =  custom.getProperty(keyStr);
              setProperty(ltiProps,"custom_"+keyStr,value);
          }           
  	}
docs: Place the custom values into the launch