The 'research' level for Far Cry emerged on the interweb over the weekend (cheers Shadrach) for download and can be pasted into your demo installation.
The download weighs in at 37.1MB, and must be extracted to your "/FarCryDemo/Scripts/MenuScreens/" folder. Apparently this will overwrite the existing demo map, so back up the existing one if you want to go back to it later.
It's not entirely clear why this hasn't been 'officially' announced by Crytek and Ubisoft yet, but we expect they will get around to spreading the good word very soon. Until then, enjoy.
Far Cry is due out on March 26th, and we'll be reviewing it as soon as we humanly can.