Just keep the extra 4 on your counter. At day 8 when you candle your eggs, you may find some not developing at all. At that time you may decide to replace those with the ones you have in reserve. Yes, you face a staggered hatch, but that is not really a big deal. You just will have some of your chicks a week older than others.
that all 4 hatch... that equals to about $37.50 per chick. I think its an EXCELLENT VALUE. 
Close of day 20 and not a pip yet.