I'm working on writing a batchfile to be run from the XP command
prompt, to encrypt a file automatically. I need the encrypted file to
be an executable, this way, the file can be opened by the appropriate
user(s) with a shared password on any XP machine. For this reason, I've
chosen symetric encryption with GPGShell or creating a Self-Decrypting
Archive with PGP.

One switch which works with GPGShell: GPGTools /encrsfx creates an
..exe file with symetric encryption.

Here's the problem:
Running that command brings up a window that looks like this --
You have to enter a one-time passphrase for symmetric encryption.
Enter passphrase:

Is there a way to add a password into the batch file so that the
encryption process can be fully automated?

I've messed around with a few options, but haven't been able to get any
to work without human intervention.

--passphrase-fd and PGPPASSFD
look promising. Does anyone have any advice on this?