More templates customizable

Hi,
i have a website in which i use ckeditor.
I want that a logged user can use default templates and his customized template.

I put default templates in /upload/default_templates/site_default.js

CKEDITOR.addTemplates( 'default',
{
  imagesPath : CKEDITOR.getUrl( CKEDITOR.plugins.getPath( 'templates' ) + 'templates/images/' ),
  templates :
    [
      {
        title: 'Default Template 1',
        image: 'template1.gif'
        ...
      }
    ]
};

I put customized templates in /upload/USERNAME/editor_templates/site_default.js with a code like the previous one.

In config.js i put the following code:

CKEDITOR.editorConfig = function( config )
{
   config.templates_files = 
   [ 
      '/upload/default_templates/site_default.js',
      '/upload/'+frm.sia.value+'/editor_templates/site_default.js'
   ];
}

where frm.sia.value identifies user logged.

With such code, i can use only templates included in last path ('/upload/'+frm.sia.value+'/editor_templates/site_default.js').

If i write:

CKEDITOR.editorConfig = function( config )
{
   config.templates_files = 
   [ 
      '/upload/'+frm.sia.value+'/editor_templates/site_default.js',
                '/upload/default_templates/site_default.js'
   ];
}

i can use only templates included in '/upload/default_templates/site_default.js'.

What's the problem?

Thank you in advance for your support,

Giuseppe