I don't see a way to do this, even using Custom Search and negation.
My purpose is to find bugs with certain other characteristics that I'm not already getting bugmail on, then to add myself to their CC lists so I get bugmail for them.
It seems that the Custom Search "CC" entry searches for "any user on the CC list that matches". But I need it to look at the entire CC list to see if I'm on there.
I'm using Bugzilla 4.0.7, but we'll upgrade eventually so a 5.0-only solution would be okay.
I think the steps below might help you, it's important to try it using Internet Explorer browser:
1) On "Custom Search", select all available status for "Resolution"
2) Check the options for CC, Reporter, QA Contact and Assignee, leaving blank the text box where you normally input the email.
3) Click on "Search"
4) In the results page, scrolled down the page until you find "Change Columns" button and I click on it.
5) Select CC, Reporter, QA Contact and Assignee and click on "Change Columns"
6) Back on results page, right-click the page and click on "Export to Microsoft Excel"
7) Then on excel you can make the filter you want to and find the bugs you are not related to.
Please let me know if that helped you.