I love genetics, so it's easy for me to say this -- but read posts on this site about barring and cross breeding. It will take several generations to get something that looks and acts like a cuckoo brahma, but it certainly is possible. I'm not an expert on Brahmas, so I can't say exactly how the breeding plan should go, but I can tell you it will be faster to start with a male barred bird, so that both sexes have barring. Barring is sexed linked and a barred rock hen to non-barred roo will produce only barred males. Those can then be bred back to brahma hens, but a BR roo will produce all barred chicks.
Do read up on this first if you can, it can save you a lot of time to understand what you are trying to do.