I couldn't test this and only showed you what I read from the manpage.

Personally, I use a pipe through GPG like this:

my $GPG_cmd = "/usr/bin/gpg --homedir . --keyring pubring.gpg --secret
+-keyring secring.gpg --batch --trust-model always -z 7 --no-secmem-wa
+rning --lock-never";
open my $gpg, qq(| $GPG_cmd --output "$OUTFILE")
    or die "Couldn't launch $GPG_cmd: $!";
print $gpg $mydata;
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