I have found cool pop-up alert notification for OUT OF STOCK stock product. You can find demo at http://shopping.indiatimes.com/mobiles/xolo/xolo-q3000-white-/41839/p_B2362026
Just scroll down the page & it will show pop-up alert to subscribe for product availibity. Further more you can add feature in popup like "subscribe & get 10% discount" when this product available again.
I guess it will be great sale booster as customers will prompt to subscribe if some discount is available for product. You can further custmze the module like first 10 subscribers will get 20% discount & you can display stats like "Only 3 more customers will get this offer" if 7 people have already subscribed for the product notification.
I don't know you can add this feature in your module or not. I am just sharing the idea