interesting, I didn't know about that. You still end up having to do a toString override to properly suppress the 'undefined' return value though:

    window.__defineGetter__('help', function () {
        console.log('I\'m here for you'); f = function() {}; f.toString = function() {return " ";}; return f;
    });

But __defineGetter__ would let the execution of the command work in other places than the JS console, so that's cool.