I'am not aware of any db based autoresponder patch for postfix. Autoresponders are normally generated by the lda (maildrop or dovecot deliver). But thats a different kind of setup.
A setup with postfix virtual mail users and a lda for autoresponders and email filtering is e.g. used in ispconfig 3 (perfect server guides). But you would have to reinstall the server to use such a setup as it is different in severalpoints from your current setup.