private files for public items

I've been helping a rural museum launch an Omeka-based site for its digital collections as a summer intern. We want to include both access (low-res) and archival (high-res, large size) files for some items, and we'd like to make the latter private so they can only be accessed by folks with researcher user privileges or better. I know how to do this by creating public and private items for the same thing, but it would be better if there were one public item with two associated files, one private and one public. Is there a way to do this?

I do not think there is a way but I use a peculiar way to store materials associated to an element that I do not want to be seen but I need to keep. I use the ÍtemRelations plugin for this. Basically, I créate an ítem that contains the file I do not want to show, and set it to private or non public. Then I include a RleatedItemt link to it in the original element. This link will not show up unless you are logged in as the administrator.