Here's a couple things you can try...
1. Curtains covering the front of the nesting boxes, with a slit in the middle to allow the hen in and out. By "hiding" the nest, the idea is to keep other hens from knowing there's been an egg laid and cut down on curious onlookers.
2. Wooden/Stone fake eggs in the nesting boxes, peck, peck, peck, won't break, so hopefully discourage from pecking on the real eggs.
3. Blow out the contents of several eggs, fill with spicy mustard and seal with little pieces of tape. Put them in the nesting box, hens try to eat, encounter mustard, chickens HATE mustard.
Hopefully others will have more ideas and I would try increasing their protein/calcium intake as a previous poster suggested. Good luck! That's super frustrating.