I'm making a bob the builder cake...so far I have made Rolly and some hedgehogs, a saw and a screwdriver all using sugarpaste! But it's not going to hold its shape well enough for making Bob, I really want to make him with Modeling paste, and have got some of this sugarcel powder, but there are NO instructions on the container! Does anyone know how much to use, or have a good recipe for modelling paste?