You can add your file in the folder components/com_hikashop/views/product/html/ and make its name start with listing_ and it will be added automatically to the dropdown selection.
However, if you use joomla 1.6, the installation process of joomla removes the whole component folder before installing the new files so you would loose the file when you update. That works fine with joomla 1.5 though.
The solution should be easy... Just changing the file administrator/components/com_hikashop/types/item.php to add the views folders of the main template. Do you see what I mean ?