Best way would be to use a module for example Acy Mailing or any joomla form module in this place. You just need to remember to use a syntax provided in demo content.
For start just publish an AcyMailing module there and see how different it is. I think it will not differ much, but if it does than You can always adjust the layout in it's template file /modules/mod_acymailing/tmpl/default.php by making an override and copying this file to to template's /html folder /html/mod_acymailing/default.php