You _should_ be able to go to your game installation folder (probably C:\Electronic Arts\Crytek\Crysis 2) and open system.cfg in Notepad. Then add the line con_restricted = 0 and save.
It goes without saying, of course, that you should have exited the game beforehand.
I can confirm that this method will not work. The game will register the command but it will not unlock all the console commands. Also, cheats will not activate if you put them into the autoexec.cfg file.