Temporary symlink in shell - "named process substitution" - rename a file without creating a copy/symlink on the disk?

Thunderbird doesn't open files that don't have .eml extension as email files, but instead starts to compose a new message and adds them as attachments. To use thunderbird in scripts I'm looking for a way that would allow you to "temporarily rename" a file as a file.eml, open it in thunderbird (possibly edit, but at least read) and close it without saving anything to the disk - all in that process' memory. While this could be achieved by either copying it or creating a symlink to that file in a temporary location there are many elegant ways to use process substitution or here strings that instead create "temporary files" in RAM that live only for duration of the process. Is there anything that could create such "pseudo symlinks" in bash/zsh?