Save New Camera Raw Defaults did not work for me either. After launching ACR via Photoshop CS6, I changed Process to 2010, Camera Profile to Camera Neutral, and saved it as the ACR default. After relaunching ACR, Camera Profile defaulted to Camera Neutral, but Process reverted back to 2012.
My suspicion is that Adobe is passive-aggressively attempting to force migration to Process 2012. With ACR CS5, a previously unedited RAW image defaults to Process: "2010 (current)", with 2012 listed as an option. With ACR CS6, the same unedited RAW image file defaults to Process: "2012 (current)", with 2010 listed as an option. Evidently, the "(current)" label has nothing to do with the file's metadata; it indicates which Process that version of ACR will use as its default.
So to answer the OP's question, the only way I can see to have ACR default to Process 2010 is to launch Photoshop CS5...