Bonding two part alginate molds...

I am not trying to cut corners, but make things easier for the models I use. Some of them tend to get a little antsy towards the removal phase of the molding process. I need to find a way to remove the alginate molds better. I have seen head castings where the alginate is cut down the center on the backside of the mold. Once it is seperated, how does one re-bond or rejoin the alginate?

For instance, if I am wanting to do a complete abdomen section using the alginate, say Moldgel or Fibergel, I apply it either by hand or using a model box, and the model's body above and below the ab section is larger, I risk ripping the alginate. I am assuming I would cut the back section down the center?? But when pouring in CastRite material, would it not leak out if the alginate is not rejoined?