this article points out -- check out the "Warnings and Instructions" section). However, you may have trouble protecting the legally mandated requirements of the insert if, as you note, there are limited ways to express the statement. When that's the case, the merger doctrine kicks into effect and others can get away with copying.
What about adding 'copyright reserved'? You can add any wording you like about copyright being reserved -- that may scare off some interlopers -- but that doesn't necessarily mean that a court will enforce your claim to copyright. It will all come down to whether you've demonstrated sufficient creativity and can justify your exclusive rights to the work.