Adding an instrument halfway through

I'm creating a piece with 4 vocal lines but it starts off with just one voice. I would really like to have just the one voice on the score and then split into 4 on another page. Is there anyway to do this? At the moment the other 3 lines just have rests and it'll be a waste of space when I print it out. I've had a look online but I can't find anything so any help would be great.