How good are you at scratch building?
Essentially, every model ever hand sculpted is the process of building up epoxy putty over a structure, so the scope of your idea could range from utter disaster to award winning triumph!
I'd recommend some wire, rather than sprue, as a scaffold though, will make getting the shape easier.
This is what I was thinking they might be based from earlier, you can pick these up from bits sellers, they're popular, so not especially cheap, and often sold out, so you have to be patient, but if you're not confident with scratch building, they might be another way to go.