You will build up to it. I promise. At first it almost seems like you're doing push ups. I think you will be surprised how quickly you pregress. Because it's alot of negative at first, you will be ripping the muscles something fierce. Be sure to let them heal, and I would advise NOT going to failure. Let yourself completely recover before you do it again, and since you're not going to failure, hopefuly that won't be too long.
You can also start these out as static contractions to get used to it.