special_use folders

My setup is postfix mail gateway/spamassassin on one machine and dovecot mail box server on another machine.

Will the following configuration work?

1. On the mail gateway, I install dovecot-lmtp and use it to deliver locally spam.
2. On the mailbox server, I configure special use junk folder to point mail gateway's spam folder via nfs.

If this is correct, how can I configure special use folder to point to a path (variable based on email) which is different from default path?

If there is a different way to handle this, I would interested.

Thanks in advance