I know how you get Exxon (or any other polluter) to never under report their leaks again.
You fine them Millions of dollars every time they do. It is the only way.
What you do not do is let them laugh at us all: just invite their scientists to have a "sit down" with reasearchers to see how the company might ("MIGHT"!!!) avoid under reporting methane leaks in the future??. They are having a LAUGH!
We are doomed unless there are consequences and everyone takes responsibility for their polluting for once.