This won't happen as long as the worst offenders can push individual arbitration agreements. The Supreme Court heard arguments about them recently, and a decision on whether they are legal is expected soon.
On the other hand, electronic health records should make it easy to show with statistics if a workplace causes chronic disease, relative its peers. We just need to add employer information to the standard information that hospitals collect. Certainly a group of university hospitals would be interested in seeing this data, and could organize an initiative to collect it.
Edit: Actually, a way to link massive amounts of healthcare data to patients' employers might already be available. Medical records often store insurance information, which can be used to figure out a patient's employer if they are the subscriber.