Where to put file? Fixing another contribution

I tried posting this in the 'Contribution Writing Guidelines' forum, as it seemed the appropriate place, but there's low traffic there; perhaps someone over here has an answer =)

I'm fixing up another user's contribution (http://www.zen-cart.com/index.php?main_page=product_contrib_info&cPath=40_62&products_id=994 -- updating it to 1.3.8 and fixing a bug), and figured I might as well go all the way and fix it up to normal standards and re-release it.

One of the files in this contribution is in the root directory, which is obviously not a very good place for it, but I'm having a hard time figuring out a reasonable place to put it instead. This is a php file (not auto-loaded) that is referenced by a javascript file (which is auto-loaded). Files in 'extra_datafiles' are auto-loaded, so that folder is no good. It won't work in the base includes, modules, or templates directories (forbidden). I thought it would work in the YOURTEMPLATE/templates directory, but it won't work in there either.

The file is sort of a template file, but since it's called directly from a javascript file and not loaded in the same manner other templates are, I guess that's why it throws up Forbidden errors when you try to access it in most folders? Specifically, this file contains what the main image section of a product info page is replaced with when a user changes attributes.

Is there actually a place to place this type of file that I'm missing, or perhaps a different way to go about it? Even if I try just making a new directory for it, that doesn't work either...