The first step was to build up a wall of clay that covered the sculpt half way up. The hardness of the frozen hands meant i didn't nick or damage the sculpt as I was applying the terracotta clay.
Above is a picture of the mould box filled with PU resin. This is the first half of the mould done.
After the resin was dry removed it from the box, flipped it, and removed the terracotta clay leaving the hands still in the mould. After adding more Plasticine keys to the resin surface, and building a new box, I poured the second half of the mould.