[Dovecot] pop-proxy to redundant servers ?

I'm considering putting two servers with failover IP-addresses in front of our pop/imap cluster, with dovecot in proxy-mode running on both servers. But, can dovecot handle more than one backend server for each user ?

I.e. I would want to point the dovecot proxy to send userX to backend-server1, or backend-server2 if backend-server1 is down. Is something like that possible ?

-jf