Advertising can do this in one of two main ways. First, it can emphasize the positive effects of buying the product that is, at this point, undesirable. Second, it can make potential customers feel that their lives will be harmed in some way if they do not buy the product.
As an example, let's look at the warranty. You could have an ad that shows someone's kid tipping their TV over and breaking it. Then you could emphasize how happy the person is that she bought the warranty. If you wanted to look at the harm that could be done if you don't buy the warranty, you could have a guy who was going to host a big party to watch some sports event on his new TV. The day before, it breaks and it's not under warranty. He loses popularity among his friends because he is not able to throw the party.
In general, you have to look for things that are positive about the product (or for negatives that occur if customers don't use it) and then play those up.