code: private static void addToSystemClassLoader(URL url) throws Exception {
      URLClassLoader sysloader = (URLClassLoader) ClassLoader.getSystemClassLoader();
      Class sysclass = URLClassLoader.class;
  
      java.lang.reflect.Method method = sysclass.getDeclaredMethod("addURL", new Class[] {URL.class});
      method.setAccessible(true);
      method.invoke(sysloader, new Object[] {url});
    }
docs: Adds the specified URL (for a jar or a directory) to the System ClassLoader. This code was
  written by antony_miguel and posted on
  http://forum.java.sun.com/thread.jsp?forum=32&thread=300557&message=1191210 I assume it has
  been placed in the public domain.
  
  @param url the URL of the resource (directory or jar) to add to the System classpath
  @throws Exception if anything goes wrong. The most likely culprit, should this ever arise,
  would be that your VM is not using a URLClassLoader as the System ClassLoader. This would
  result in a ClassClastException that you probably can't do much about.