Prototyping Object in Javascript breaks jQuery?

If it’s simply a case of messing up for…in loops, can’t you use Object.defineProperty to add your fn without making it enumerable?

So:

Object.defineProperty(Object.prototype, "foo", { 
    value: function() {
        // do stuff
    },
    enumerable : false
});

Seems to work for me. Would this still be considered bad form?