--enable-special-filenames This option enables a mode in which filenames of the form ‘-&n’, where n is a non-negative decimal number, refer to the file de‐ scriptor n and not to a file with that name.
but it fails to work for keyrings:
gpg --export $FPR | gpgv --enable-special-filenames --keyring '-&0' sample-file.asc
gives the following warning:
gpgv: keyblock resource '/home/dkg/.gnupg/-&0': No such file or directory
It appears that --keyring's weird special treatment of filenames without a / is taking precedence over the explicitly-specified --enable-special-filenames.
This makes it more cumbersome than it needs to be to build a curated keyring on the fly without touching the filesystem.