CREATE AN EXIT GRABBER PAGE (if end-user leaves the website)

I need to create an exit grabber page, which is a page to which end-user(customer) would be routed to if he leaves the website or goes to a different site. The purpose of the 'exit-grabber' page is to stop the customer from leaving and offering a discounted price. IF user decides to proceed, a promotional code (for this discounted price) will be automatically entered into the promo code field (in the registration form) please note: i dont need pop-up window for an exit grabber page. I WOULD LIKE THIS TASK TO BE DONE WITHIN 24-48 hours. i can provide screenshots or examples of websites that utilize this feature. thanks, michael