If you find anyone sharing CP,
1. get the IP number (eg. 123.45.6.789)
2. identify the owner at RIPE NCC Homepage (http://www.ripe.net/), APNIC Whois & Search (http://www.apnic.net/search/index.html), Allwhois.com (http://www.allwhois.com/), or the like. These sites will give you information about the owner of the IP address. They'll give you mail address, telephone number, e-mail address, etc.
3. E-mail them, phone them, or write to them that you know he/she is sharing CP, and that you are prepared to take further action when you see them sharing again.

If the recipient of your notice was THE person who was sharing, it would give him/her a scare, better yet, if your mail reaches the company, school, or any other institution to which the guy belongs, there's a posibility that he/she will be sacked for using public network for personal, and filthy purpose.

So, have fun.

You can also post the IP address here, but it's likely that the moderator will edit it out. Pity, really.