Faking a file on a filesystem

I have a need for a way for a regular user (i.e. non root) to "override" a file on a filesystem with one of their own, but just for the lifetime of a script. I'll give you an example. One of my users runs a program which is distributed in a package (i.e. not changeable by them). That program is looking for a file, /path1/file1. My user would like to change this file to a different version of the file in different scripts. I'm not aware of one, but is there a way to redirect file open calls for /path1/file1 to /path2/file2 in a script? It only has to be for file open/read calls, and not write. The /path1 filesystem is not writeable by the user. Is there maybe a FUSE filesystem which will allow this, or something else? Cheers, Sean