How about a lead strip? maybe you could drop it in the mold and then pour the foam around it?
Also, I was thinking about carving a few large BBills to act as "head-birds" for the long lines. I didn't want to carve heads so I was thinking about just incorporating the head and cheeks in a very squat position into the body of the bird. I could make it look more pronounced with paint.
If you could find a way to do this with divers, just incorporate the head into the body, you could avoid a separate head. I've seen it done with other foamers, always divers, resters and sleepers to keep the head low, otherwise it would be brittle...
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