Configuring local mail accounts on a mail-filtering proxy

I have a postfix-installed machine acting as a spam/virus filtering
gateway to my local network. I would like to create two accounts
(spam@ and notspam@) on that machine for the purposes of training my
spam filter. If the filter is currently proxying mail for the entire
domain, how do I configure it to store mail for those two accounts.
It is preferrable that I not have to make serious DNS or MTA
modifications to the rest of my network in order to effect this
solution.

Best Regards,

Gary

PS: If someone has already addressed this issue, I would greatly
appreciate a link. I've googled for this issue extensively and
haven't found the answer.