Some of the old casting books recommend using a piece of a green
branch as a stirring rod in molten metals so maybe a bamboo
chopstick might work fine.
Using a green stick to stir molten lead blinds fishermen every year
making weights, the steam generated causes an explosion and blows
the molten metal all over the room. I have seen metal explode out
like this when poured onto plaster that had not bee fully dried out,
so I suspect that using a green stick might be dangerous. A nice
dried chop stick however, as does a pencil, makes a good stir stick.