Book a last minute cross country flight on a full 737 or MD-80, put the phone in your pocket before you board, make sure you are in the middle seat between the two largest people on the plane and it should heat up pretty good with little to no effort. That usually works for me and it saves the battery because it is airplane mode.
I think Apple deleted the "heater option" in the 1.1.1 update. The glitch they are working on is the ability to toggle the heat, and set the temp.
Don't despair, the reason for the SDK is so third parties can work on the issue and bring it back. However, Apple will be licensing the feature, so they can collect a royalty, so I'm sure it won't be freeware.