Wouldn't having a list of un-whitelisted smtp servers also help... or is the concern that the email would be blackholed and simply never be delivered, exposing your scam?
Don't you also want a fake UTF16 version of their email address that bounces... so that everybody else who looks thinks they were in the CC list?
Corrupted email in the CC list could be the best strategy.
Other people can vouch that everyone was invited, and there is no weird spam text mail left that could get displayed in unexpected ways (if they try to forward it to some other mail for instance)
Don't you also want a fake UTF16 version of their email address that bounces... so that everybody else who looks thinks they were in the CC list?