Yeah I was doing that, but then I cut one and it bled out.
Have you tried holding the pea in one hand while twisting the shell in the other several times, wait just a bit, then cutting the cord as close to the shell as possible?
Take this with a grain of salt as I haven't hatched peas before (yet, lol), but what I found when incubating my Calls and turkeys is that the ones that hatch with navel/cord issues are usually the ones where the CAM never fully encloses inside the shell... the veining network that spreads from the embryo out... using on end turners is when I have found it doesn't finish enclosing properly more often as well... I switched over to using my Leahy, running it completely dry from set to hatch, and just rolling the eggs around a bit a few times a day and got the best hatch rates without major issues... it runs at 30 to 40% humidity...