I found this response under the help section on my CBS League's home page. I think this is should help.
How can I participate in the $50 per league referral offer for 2008 Football Commissioner?
It's Easy! Once you have paid for your 2008 Football Commissioner league, all league members will see -- within the "Message Center" on the League's Homepage --information on how to refer a friend.
Please Note: It is important that the friend you referred uses the unique URL that is supplied in the received referral email. Once a new league is created, the unique URL identifies the league as your referral. There is no limitation on the number of leagues you may refer.
Click to read the details referencing the terms and conditions associated with the referral program.