Yup. They can't primary him because the blacks et al would burn the place down.
The only hope they have of getting rid of him and keeping their hands clean is if he pulls a Lyndon B. and resigns or if they take him out the back door - perhaps by exploiting one of the brewing scandals (Solyndra, Gun Runner etc.)
Otherwise, as you point out, they're stuck with him.
He’ll never pull an LBJ; his malignant narcissism won’t allow for it. The only way he’s going before his term is up is if a “medical” reason crops up between now and 06 November 2012. Solyndra and Operation Fast and Furious (among others, without getting into the unfortunately radioactive “birther” angle) won’t gain enough traction quickly enough to bring his pResidency down either, IMO. At least not in a manner that results in his leaving office before his term expires. More’s the pity.