You are correct.  Although Mac OS X allows you to remap the <kbd>control</kbd>, <kbd>caps lock</kbd>, <kbd>option</kbd>, and <kbd>command</kbd> keys, the <kbd>fn</kbd> key is not included.  To do this, you'll need to use 3rd-party software such as [DoubleCommand][1].  That will let you remap the <kbd>fn</kbd> key to the <kbd>control</kbd> key.  

From there, you should check out additional software to remap the <kbd>control</kbd>+<kbd>J</kbd> key etc. to emulate the left key etc. So long as you can emulate <kbd>ctrl</kbd>, you should be able to create the keybinding in ~/Library/KeyBindings. You might be able to do this last step in DoubleCommand as well.


  [1]: http://doublecommand.sourceforge.net/