So I've got a new Acer notebook and the keyboard is laid out like this:

I want to be able to change the left and right arrows of the numpad to volume down and up and the 5 key to mute but still be able to keep the 4, 5 and 6 when numlock is on.
I've tried using KeyTweak but it doesn't know the state of numlock and the key's functions. The default volume down, up and mute keys can only be used with the Fn key. It'd be nice when random music or videos start playing too loud to be able to just hit one key to change the volume. Windows 7 btw