Do you want a built-in function to return some other variable than those it does return? While you could hack the code, that is almost always a bad idea.
Unless you know enough to have written the code yourself, then hacking supplied code is almost always going to be a source of likely future bugs. And if you could write it yourself, then you would and not have to ask the question. You could either compute what you want on the side, or write the code yourself anyway.
