Summary

print it (the finer the better, 0,2 works good) and cast it in a high temperature silicone.

You should be able to cast 12 MAMBA ballast pieces from lead in a single step.
Its a bit tricky to get them out of the frame, but as long as they are heavy they work just fine :)

Maybe there will be a version #2, which contains better canals to spread the lead more evenly.