I'm not sure weather it'd have the shure strenegth required when you come to de-mold the bio. You could do a latex snap mold or has been said in previous threads molding silicone or silicone caulking, you can add acrylic paint to the caulking to get it to kick a mite quicker too. Sometimes it's worth doing something on the cheap, and then there's the times it's worth doing properly. Personally I would plump for the caulking for a first time mold like this, it is cheap and pretty easy to do a brush up mold. Just remember to where gloves. You can make a mother mold for the finished silicone mold from plaster bandages to stop it from warping when you cast the final piece.