How to add automatic Live Demo Button in woocommerce

I already set up my ecommerce shop to sale digital products by using woocommerce. Now to show my product demo, I am trying to add a Live Demo Button before add to cart button in Woocommerce single product page.

I can do it easily by using bellow code:

//add live demo button to single product page

function shameem_before_add_to_cart_form() {

    global $post;
    $demoslug = $post->post_name;
    $demourl = get_bloginfo('url').'/'.$demoslug.'/';
        $demotitle = esc_attr($post->post_title);
    echo 'Live Demo';
}
add_action('woocommerce_before_add_to_cart_form','shameem_before_add_to_cart_form');

If I used those code, then my Live demo button url will be: http://ift.tt/1u7s6eP

But I want live demo button url will be http://ift.tt/1yGrhGq

Is there any other way I can do what I am expecting, or any modification that can change my url to demo.siteurl.com.

Here is an image about what I am looking for:

Any help will be appreciated. Thanks