Superchips tuners can disable it, contrary to what others say. Speaking from experience. Had a Superchips Cortex 2950 for my 2008 Impala SS LS4. Best purchase I ever made. Not sure if they're compatible with the 3.9L though. Range will also disable it.
In my case with the 5.3L, my mpgs went UP running 8 cylinders full-time. This was tracked over 6 years. I had excessive oil consumption too. 1 quart every 750 miles. Immediately after the tuner, consumption went to zero. Didn't lose a drop for years after, including the day I sold it.
Just be aware that unless you *physically* remove the AFM components, they can still fail, even if they're never in use. So please maintain it still. Not sure if the 3.9L has a "Valve Lifter Oil Filter" like the LS4, but that little filter is crucial to AFM health.
Good luck, they're great cars minus AFM, the air door actuators, and the delicate 4T65. Which reminds me, when was your last trans fluid service?