encrypt only the body

Moin,

I encrypt and forward emails to a specific user with
procmail and this receipt.

:0b
* ^Subject:.*TestMT
| gpg --encrypt -a -r user | $SENDMAIL -oi email(_at_)domain(_dot_)foo

Is there any posibility to encrypt only the body
and preserve the subject line. All email for this user
should automaticly encrypted.

Bis dann
Matthias