Sounds like a good application for a tarpit, i.e.:
http://www.spamcannibal.org/
Good idea. Alas, the FC2 kernel lacks the netfilter tarpit module. Otherwise I could say something like "iptables -s nasty-spammer -j TARPIT". That'll tarpit any TCP connection coming from that address. (SpamCannibal wraps a DB around this, populating an iptables chain with new entries as needed.)
Some stuff on the TARPIT module:
<http://www.netfilter.org/patch-o-matic/pom-extra.html#pom-extra-TARPIT>
<http://www.securityfocus.com/infocus/1723>
