I finally got frustrated enough to risk calling Ford customer service (risking even more frustration). I was lucky enough to get a sympathetic agent who was willing to dig deeper than the normal scripted responses. Apparently they have multiple systems that show upgrade availabilities. He check a couple of them at first and they said there was no upgrade for my car (just like Ford's Sync website). But then he went on to check another system called PTS and it shows that there is a dealer-install upgrade "Gen 1 version 3.1.4" available for my car. He said I should call the dealer and ask them to download the update from PTS and install it for me.
I will be taking my car to the dealer next week to see if it works.
I'll admit that I had to stretch the truth a little to get him to look deeper... he asked if I got my information from some online forum and I told him that I had seen it working on a 2011 at the local Mustang club meeting.
2011 Pony Pkg. convertible M6
Am WS7 (sold)