AdditionalParticipants.tpl custom template is not being loaded for a specific Event

I have created a custom template folder at the following location:
../civicrm_custom/CRM/Event/Form/Registration/1/

The "1" folder is in reference to EventId #1.

I have placed 2 files, Register.tpl and AdditionalParticipants.tpl in this folder. Register.tpl is loading correctly when I goto register for this event, however the AdditionalParticipants.tpl is not. I have cleared out the templates_c folder and it still will not load. I have loaded the Smarty Debugger, and the variable $tplFile is pointing to the out-of-the-box template.

I'm running CiviCRM 2.2.2 on Joomla 1.5.10.