public class SCI implements ServletContainerInitializer {
  @Override
  public void onStartup(Set<Class<?>> arg0, ServletContext arg1)
    throws ServletException {
    arg1.addFilter("myFilter", MyFilter.class).addMappingForUrlPatterns(null, false, "/*");
  }
}

public static class MyFilter implements Filter {

  @Override
  public void destroy() { }

  @Override
  public void doFilter(ServletRequest arg0, ServletResponse arg1,
      FilterChain arg2) throws IOException, ServletException {
    if (arg1 instanceof HttpServletResponse) {
      ((HttpServletResponse) arg1).addHeader("Test", "Test");
    }
    arg2.doFilter(arg0, arg1);
  }

  @Override
  public void init(FilterConfig arg0) throws ServletException { }
}

test.SCI

<featureManager>
   <feature>bells-1.0</feature>
</featureManager>

<library id="init">
  <file name="path/to/jar"/>
</library>

<bell libraryRef="init"/>