[OS X Emacs] use system input source shortcut in Aquamacs

[Max Arnold]

On Tue, Feb 14, 2012 at 10:15:21AM -0500, David Reitter wrote:
> I suggest you simply write a function that switches the Emacs input language, and also executes the changeInput program

Is it possible to bind this function to OS X default system-wide shortcut (Command-Space for example)?
Or even better, use CapsLock as language switcher in any OS X application including Aquamacs?