exactly it's a manga which means nothing has to make sense. if he doesn't use the clones then there is no way he can complete this training before pain attacks konoha, especially if jiraya couldn't master the tech.

On another note wtf happened to the scroll with narutos key, they just completely threw that out the window. I was expecting some training dealing with that since jiraya said the 4th left that behind so naruto could learn the powerful tech the 4th did not complete. so if they bring that out at some point expect another power up.