RUMFITS, my dealer Criswell Chevrolet in MD that I bought from does Mobil1 no extra charge. Call Paramus Chevrolet and talk to SERVICE MANAGER. Tell him you are buds with me and are looking to find a service dept to have a long term relationship with, but that is contingent on getting the Mobil1 with your free 4 oil changes. He put the warranty service ticket in on my change, and as long as he was paid by GM to do the work, should not be an issue. If he didn't get paid the difference, he might not do it.
Also, it might be contingent on having a Z51, which mine was.