You have to undersand crabs to get them to peel in a tank. Crabs you will be surprised to hear have their skeleton on the outside, now that causes problems when it comes to the birds and bees bit of crabbys life. The male has to have a new dangly bit to be able to mate so as soon as the temperature of the water is high enough he peels to get ready for loooooooove, first in the queue. He can do this about twice a year on average as loosing the shell and creating a new one takes a lot out of him.
Now he has his new bits he goes in search of a female. The females send out a scent into the water, Pheromones, that tells the males she is ready to peel. Whilst she is in her armour it works like a chastity belt, males cannot mate but as soon as she sheds the shell she can which is why you get a male carry a female round. She will allways be a peeler or a softy.
The peeling process is temperature dependant as they need warmth to harden their shells off, that is why you quite often find a softy just under the weed, it is warmer than in water or tucked under a rock.
What you need to do is create a tank with warmth, shelter and oxygenated sea water. Put crabs in there that have not peeled yet this year and you will make them peel. Check them every day and you will find the ones that are popping. You take these out and put them in the fridge. This slows down the process and holds them at the popping stage. If you leave them in the tank they will peel and suck in water to expand their soft shell to leave room for this years growth. That is why softies are so watery and peelers are so concentrated as they expell water to shrink the new soft shell away from their old one.
Fish must be able to sniff out the pheromones the females release which make peeler such a good bait. Once the female has shed the shell she stops making the pheromone as within a couple of tides she will be in her chastity belt again and not able to mate until the next time she peels.