Use pre-cut plaster bandages for the support shell which will be built in two halves. The first step is to create a parting line along the high point of the model's head. When applying the plaster bandages, be sure to NOT cover the breathing holes for the model. (In this application, the model is breathing through his nose.)
Prior to applying the second half of the support shell, apply a layer of petroleum jelly to the seam line to serve as a parting agent between the two halves. Build up more plaster bandages on the back of the mold.
After the plaster bandages have been completely applied, it is necessary to let the bandages cure solid. This will usually take about 7 - 10 minutes. Once the bandages are fully cured, the support shell can be removed.