Examining a backup -- any way to do this?

I have a user-entered text field that specifies the filepath for the next backup copy of the database file (using Save a Copy as ["$$Backup"; copy] with $$Backup loaded with the filepath) of a 2-file separation model.

Immediately before writing each backup, I want to examine any existing backup in the path by importing some key identification parameters to display for the user -- who can then decide whether to proceed.

The problem is that FileMaker won't accept the $$Backup as the specifier (like it does for imports and exports) of which file to open. I want to avoid requiring the user to respecify the path, since it's sitting in a field on the screen. Plus, I like to run everything automated, with no dialogs required.

So is there a way around this restriction? Or maybe a different approach to getting at the parameters in the file? Being my first attempt at this, all suggestions are welcome.

Thanks for any help.