You're screwed.
You can't refi with BMWFS. It is now a "Pre-Owned" car to them and does not qualify for the 3.9 percent rate. As a previous poster said, you can refi it with someone else as a "pre-owned car". They will have to run your credit and approve you based on their requirements. I don't think you'll beat the 4.9 tho. USAA is for military people only. With the current rates it is likely the only banks that would beat it would be USAA or Navy FCU (special govt related banks).