Building WebUpdater fails in library code...

Another question:
Is there some way to customize the firmware update webform?
The source of the form page looks like this:

<html><body><form method='POST' action='' enctype='multipart/form-data'>
                  <input type='file' name='update'>
                  <input type='submit' value='Update'>
               </form>
         </body></html>

I have tried to locate where this is created but failed so far.
I would like to add some text and also a title to the webpage, so I need to find exactly where it is defined.
Any ideas?