A Better Way to Advertise

Wonder if companies already do this:

Put your ad on your website and use your server to randomly insert some keywords or numbers into the add at randome times. Ask viewers to note those down. Then, your server notes down the IP address - uses an IP address locator to get the zip-code of the viewing computer and the time (zip code, time, random keywords provided). Then, you tell your viewer that he can get a mail-in-rebate if he uses the keywords provided when making his purchase.