Grégoire Michel I definitely agree that modifying the SFDC setup to no allow opptys to be created/closed/moved stages without these types of roles is best practice, we're definitely moving in that direction but haven't got the buy in from management as to the necessity of making it required. My hope is that by running some automated email programs to customers that we can show why this is an essential practice and should be mandated and not simply strongly suggested and checked manually by CS.
I think that Sanford Whiteman answer
Therefore I think an SFDC-side trigger on Opportunity is the solution. Don't let the Oppty get closed unless business criteria have been met -- either with the current Sales Closed field or a secondary field dedicated to this flow.
is ultimately the "correct" answer from a fundamental perspective, but think I will see what Devraj Grewal 's idea with the batch campaign yields.