[exim] moving spam to a different folder

Hello all, is there any way to move spam marked messages (reading the
spam headers) to a different folder than new inside the user maildir?

Fact is, some users still use dialup and other users use gprs/edge to
read their emails.

First group has the speed problem.
Second group is charged by the transferred kbytes.

So what i want to to is to move out the marked spam to a different
folder reachable by imap and leave the inbox that read's the pop3
clients with the non marked email.

Any help?

thanks in advance.