You could try KeyRemap4MacBook:
or FunctionFlip:
If neither works, you could also try creating a private.xml in KeyRemap4MacBook:
<?xml version="1.0"?>
<root>
<item>
<name>Change F-keys</name>
<identifier>0A0FE074-9C9C-43DC-8AEB-6683C5CB3259</identifier>
<autogen>--KeyToKey-- KeyCode::F1, KeyCode::BRIGHTNESS_DOWN</autogen>
<autogen>--KeyToKey-- KeyCode::F2, KeyCode::BRIGHTNESS_UP</autogen>
<autogen>--KeyToKey-- KeyCode::F3, KeyCode::MISSION_CONTROL</autogen>
<autogen>--KeyToKey-- KeyCode::F4, KeyCode::LAUNCHPAD</autogen>
<autogen>--KeyToConsumer-- KeyCode::F5, ConsumerKeyCode::KEYBOARDLIGHT_LOW</autogen>
<autogen>--KeyToConsumer-- KeyCode::F6, ConsumerKeyCode::KEYBOARDLIGHT_HIGH</autogen>
<autogen>--KeyToConsumer-- KeyCode::F7, ConsumerKeyCode::MUSIC_PREV</autogen>
<autogen>--KeyToConsumer-- KeyCode::F8, ConsumerKeyCode::MUSIC_PLAY</autogen>
<autogen>--KeyToConsumer-- KeyCode::F9, ConsumerKeyCode::MUSIC_NEXT</autogen>
<autogen>--KeyToConsumer-- KeyCode::F10, ConsumerKeyCode::VOLUME_MUTE</autogen>
<autogen>--KeyToConsumer-- KeyCode::F11, ConsumerKeyCode::VOLUME_DOWN</autogen>
<autogen>--KeyToConsumer-- KeyCode::F12, ConsumerKeyCode::VOLUME_UP</autogen>
</item>
</root>
It might only work if you use the external keyboard with a laptop or have another keyboard connected. From ConsumerKeyCode ignored - Google Groups:
KeyRemap4MacBook requires at least one keyboard with functional keys (Volume Control, etc)
when you want to change keys to functional keys.
If possible, please connect the Apple keyboard to iMac.
If you don't have another keyboard,
please use Spark or Quicksilver or other apps to this purpose.
Best Answer
Macworld explained the procedure for a unibody MacBook, but I imagine the procedure is similar for an Apple wireless keyboard:
Despite the name, this app will also work happily with non-MacBooks, or even non-Apple keyboards. I haven’t used it specifically to simulate a numeric keypad on an Apple wireless keyboard, but I have used it for other things and it generally works well.
It’s also well-maintained: the developer has been releasing regular bug fixes and new versions for OS X releases since late 2006.