While it is true that the kazakhs wanted to keep the union, let's say that the PoD is that there is a nationalist coup in Kazakhstan during the chaos of the 90s, and the new government takes a anti russian stance.
Could a random russian general desert with some divisions and brigades to a very russian populated area and seizes for it creating a quasi state, without recognition from anyone but at the same time not completely dependent on moscow? The idea is that he is being helped by Moscow, but he can defeat the assaults of the kazakh army by himself and the internal policy of the areas he controls are up to him.
A final thing: It must be on central asia, no especially on Kazakhstan, it can be a enclave on turkenstan too.