Because cocoa butter is more saturated (and therefore more firm) than the butterfat in cream cheese or sour cream, it will be tricky to work it in without changing the creamy texture. You might try cocoa powder mixed with just enough boiling water to bloom it and form a paste. Cocoa powder (even the full-fat variety) has less cocoa butter than bar chocolate, so hopefully that will have the least effect on texture. Maybe you can balance it so that the water compensates for the cocoa butter.
All that said, I must admit I’ve never tried it, as I’m not a fan of the combination of chocolate with any sort of cultured dairy. But Rose does make sour cream ganache, so maybe it would be OK?
There’s always the oblivion, for a tried-and-true intense chocolate experience