I have added this to private.xml in KeyRemap4MacBook:
<autogen>__KeyToKey__ KeyCode::COMMAND_R, KeyCode::COMMAND_L, ModifierFlag::COMMAND_L | ModifierFlag::CONTROL_L | ModifierFlag::OPTION_L</autogen>
<autogen>__KeyToKey__ KeyCode::KEY_1, VK_CONTROL | VK_OPTION | VK_COMMAND, KeyCode::VK_CONSUMERKEY_BRIGHTNESS_DOWN</autogen>
<autogen>__KeyToKey__ KeyCode::KEY_2, VK_CONTROL | VK_OPTION | VK_COMMAND, KeyCode::VK_CONSUMERKEY_BRIGHTNESS_UP</autogen>
<autogen>__KeyToKey__ KeyCode::KEY_6, VK_CONTROL | VK_OPTION | VK_COMMAND, KeyCode::VK_CONSUMERKEY_MUSIC_PREV</autogen>
<autogen>__KeyToKey__ KeyCode::KEY_7, VK_CONTROL | VK_OPTION | VK_COMMAND, KeyCode::VK_CONSUMERKEY_MUSIC_PLAY</autogen>
<autogen>__KeyToKey__ KeyCode::KEY_8, VK_CONTROL | VK_OPTION | VK_COMMAND, KeyCode::VK_CONSUMERKEY_MUSIC_NEXT</autogen>
<autogen>__KeyToKey__ KeyCode::KEY_9, VK_CONTROL | VK_OPTION | VK_COMMAND, KeyCode::VK_CONSUMERKEY_VOLUME_DOWN, ModifierFlag::OPTION_L | ModifierFlag::SHIFT_L</autogen>
<autogen>__KeyToKey__ KeyCode::KEY_0, VK_CONTROL | VK_OPTION | VK_COMMAND, KeyCode::VK_CONSUMERKEY_VOLUME_UP, ModifierFlag::OPTION_L | ModifierFlag::SHIFT_L</autogen>
The first line remaps the right command to control + option + command. I mainly use it as a modifier key for opening applications, but it serves as a substitute for fn in this case. I didn't use the F-keys, because key repeat is disabled for them, and they are harder to press without looking.