Is there a way to prototype a namespace in a limited scope?

I have a prototyped function that i would like to use it in a limited scope in order to provide it with a jquery plugin.

//Prototype
function StringBuilder(str) {
    this.value = str;
}
StringBuilder.prototype.append = function (str) {
    this.value = this.value + str;
    return this;
};

//jQuery plugin with Revealing module pattern
jQuery.Rut = (function () {
    //i would like to be able to use StringBuilder only in this scope
    helloWorld = new StringBuilder('Hello');
    helloWorld.append(' World');
})(window);

Is that possible?

Thanks