After all, corruption does not just involve government. Business people and lawyers and citizens pay the bribes, even as they condemn bribery. They should be invited to become part of the solution. The first point to note is that business people and citizens know where corruption exists and how corrupt systems work. Citizens understand how bribery shapes the services they receive or don't receive.
Accountants know the illicit games played with audits and taxes.
Lawyers understand corrupt legal practices. Business people know all about corrupt systems of procurement and contracting. In many countries, if an individual stands up to denounce a corrupt system, he or she will be attacked by it. So, the trick is how to learn what people know about corruption without asking them to commit suicide. Please consider this idea.