4 days of difference is not so bad... Here's what I would do. Don't bother building a temp. incubator, those can be a lot of trouble. Instead, keep humidity as you normally would until you see your first pip. Raise humidity to 55% or so until they hatch. Chickens hatch a lot faster than, say, ducks or geese, so if your other eggs are exposed to this short burst of higher humidity, it is unlikely to do lasting damage. After your chicks have hatched, keep your humidity very low until you at least go into lockdown for the other eggs. In preparation for this, I'd keep the humidity very low, if not just go completely dry, to ensure they lose enough weight.
It is not about a daily average being met... It is about weight loss over the entire incubation period. So, you can have short bursts of higher humidity, so long as you have an answering burst of lower humidity to balance it. Make sense? I think it can be done.
As an additional thought, it would be best if, at 55%, you did not interrupt by opening the incubator much -- as little as you can, just to make perfectly sure the eggs stay moist enough. Seeing as your other eggs will be late in incubation at this point, turn once a day as soon as your other eggs begin to externally pip. One time should be fine at this point. I have even stopped turning entirely early, for eggs with detached air cells for instance, with no problems at all. Turn regularly until the first external pip when you raise the humidity, because at that point opening the incubator won't do a thing to the eggs. (Assuming you are not using an auto-turner... if so it is probably advisable you just take it out as it can be dangerous for chicks).
Also, it might be best, after you take newly hatched chicks out, to spritz the other hatching eggs. If you do take out your fan for hatch, though, that will make this whole thing easier, I should think, and you may not need to.
Yes it makes sense. I have about 30 eggs, if they all make it to lockdown, which I doubt that will have to hatch before the 14 late ones do. I will be trying to cleanup some in the bator as I snatch babies out. I have never hatched in an egg carton but I am assuming that would help cleanup too. I just don't know that I am willing to try something new as far as hatching with this batch of eggs. I have my temp set up good and never have to touch the control and I know if I put them in egg cartons to hatch it is going to take adjusting.