How to add a email address to cc field in activityparty based on the condition? They are not System Users, no contact, no account, no lead?

Hi All,

Can anyone please help me on the issue? I want to add the email address based on the condition to cc field, I know that we can manage through activityparty but it supports only for user, contact,account,lead. In my scenario they are not the above one. They don't have any relationship to CRM but I need to add their email Id's on CC list. Please suggest me the optimized way to achieve this? Thanks in advance.