I do this when I want to maximize my hatch.......
Personally I would candle and open the air sack of a couple of eggs to see if they are alive and well. If I could see them pipped into the air sack just put a very small hole or crack as close to the beak as possible. This should get them started.
Obviously toss the dead poults.
Then pump the humidity as high as you can.
Breaking lockdown is not desirable but if the alternative is "wondering if" break it. You may still be able to salvage a few nice poults.
If I'm comfortable with my incubating process, I'll manually pip (about 1/4-1/3" hole) any unhatched eggs at day #29 at the top of the large end (at the top of the airsac) , then make the tiniest hole in the membrane right next to the beak. The membrane can be very vascular, so expect a tiny amount of bleeding with a tiny hole in the membrane. A small rent in the membrane will result in a bloodbath. Remove the hatched poults, and raise the heck out of the humidity to prevent shrink wrapping (75% or so if possible- you WANT small water droplets forming on the top of the incubator). I then give the viable poults another day or so to emerge from the egg... if they don't, I then manually hatch them myself. Saved (or maybe they would have just hatched a couple days later on their own, who knows) a few poults last year doing that. And if they are already dead when you manually pip them, at least you know you didn't lose any poults that pipped the inner membrane and ran out of air before pipping the shell.