I think you can do it out of green stuff. The way it was explained to me was, you cover the thing to be moulded in a thin layer of vaseline, then press the GS around it. Then you can slip the original out when it dries. Then coat the inside in another thin layer of vaseline, and press more GS into it.
I guess you could use FIMO or something too, I can't see it making much difference.
Somebody on here will know more about it, I've not tried it myself yet. Just thought it would be cheaper and you wouldn't end up with a stack of hippos back ends with no heads on.
That would just be weird.
