Is it possible to have Dovecot imap/pop daemons listening on multiple ports?
No, not in the current stable release. But there are workarounds, eg using your firewall to redirect incoming traffic to a given port.
# Example IPTABLES, REDIRECT INCOMING CONNECTION ON PORT 9292 TO DEFAULT POP3 PORT
iptables -t nat -A PREROUTING -p tcp -m tcp –dport 9292 -j REDIRECT –to-port 110