with_scope.js

$.with_scope = function(scope, callback) {
    var $scope = $(scope),
        jquery_proxy = function(selector, context) { return $scope.find(selector, context); };
    return callback(jquery_proxy);
};

// -- or --

$.fn.as_scope = function(callback) {
    var self = this, jquery_proxy = function(selector, context) { return self.find(selector, context); };
    return callback(jquery_proxy);
};


// examples

$.with_scope('#post_15', function($) {
    $('.comments').hide();
});

$('#post_15').as_scope(function($) {
    $('.comments').hide();
});