Not making Styrofoam in the first place is a better answer.

Among other problems, Wikipedia states: "The EPA and International Agency for Research on Cancer reported limited evidence that styrene is carcinogenic for humans and experimental animals, meaning that there is a positive association between exposure and cancer and that causality is credible, but that other explanations cannot be confidently excluded." (with links to EPA reports)

A quick search found NoMoreStyrofoam.org http://nomorestyrofoam.org, which says a lot more.