I know this is an old message, but I've just worked out a way (couldn't find anything anywhere!)
I know this first part is probably not the best way of doing it, but its the only way I could think of.
All of this is the root user on the mailing machine of course...
1. Add email@example.com to the white list (thought that no one knows what the host name of the mailing machine is called!)
2. copy the blocked mail somewhere
cp /var/spool/amavis/virusmails/blocked.gx ~/mail.forward.gz
3. unzip it
gunzip -d mail.forward.gz
4. make sure that the to: line in the post is ok (some people send it to themselves and bcc the recipients)
5. send it on!
cat mail.forward | sendmail
(or if using postfix)
cat mail.forward | sendmail.postfix
Hope this is of use to some people.