There is NO WAY I can do do that for the simple reason that it is impossible to identify clone accounts with any degree of certainty. I can register one nick with a yahoo address, another with a gmail address, a third with a ymail address. Unless I register as leongsam1, leongsam2, leongsam3 etc and declare all the accounts to be mine, who's going to know that all the accounts belong to the same person.
IP addresses mean nothing and this is especially so with Singapore ISPs which route all connections through proxies. As a result, the forum server can see up to 50 connections all coming from the same IP address. In fact, my host had to modify the security settings to allow this as multiple connections from one IP address is interpreted as a DOS attack based on the default security parameters.
I have learned not to sweat the small stuff. Since I can't prevent clone accounts being registered, what's the point of trying to go on a witch hunt.