You probably could, but why the requirement to avoid a temporary file? It feels as if you may be doing some premature optimization. The operating system won't necessarily have to do any physical I/O, as the file would likely reside in RAM for the relatively short duration that it exists. If you're truly concerned about disk I/O, many operating systems provide RAM-based filesystems on which you could place your temp file.

If it's a security concern (i.e., you don't want a temporary file that *might* get written to disk), then you may have to audit emacs as well, as it may use temporary files during the edit process...and we won't even talk about the swap space....

...roboticus