At this point, you can either deal with your model to remove the baldcap and send them on their way, or better yet, do the casting of the lifecast positive first. Alginate has a tendency to shrink as it dries to some degree, so you should try to get to that as quickly as possible after doing it. If you MUST be delayed in running the plaster positive, then apply soaking wet paper towels to the inside of the negative alginate cast so it won't shrink. This is where an assistant can help in removing the baldcap from your model. But if time isn't an issue, they can wait till you are done.

If you HAD to wait to do the positive casting till the baldcap was removed and the model allowed to depart, then take the wet paper towels out of the negative alginate mold and blot out any puddled water with additional dry paper towels. Otherwise, proceed to prepare the lifecast for casting a plaster positive. Fill the nostrils - and as in this case the hole left where we had a ponytail - with dental alginate or water based clay. Apply petroleum jelly or any suitable release agent (like Tincture of Green Soap) to the inner surfaces of the plaster negative wherever there is plaster that will come in contact with the plaster used to create the positive lifecast. It isn't really necessary to apply release to the alginate because the plaster won't stick to the alginate - just to other plaster. Fit the two halves back together and secure them with Duct tape or mold straps. You're now ready to cast the positive.