There's a whole range of things no one considers when thinking about the OGL, and a lot of things you still can't legally do even with an OGL game. The best way to slip right past all of them is to simply score a Powered by Spycraft license
It requires approval but assuming what you're trying to do is supporting the game rather than undermining it that shouldn't be an issue - and best of all, it's entirely free.
We'll watch for your application.
P.S. If you're still unsure what to do, drop me a line and we'll chat about the specifics of your project.