It’s been a couple years now, but I have done this exact thing. It was pretty fiddly and slow to render, but it worked. The trick was that the light/rays combo breaks if they get too far outside the frame of your Action. I seem to remember having to build a super-sized action node with the light in frame, with my rays and source image/gobo attached, and then comp/scale/repo it downstream.
I also remember having to crank my light and sample values extremely high to get the ray definition I wanted. It was pretty frustrating! But quite satisfying when I finally got something that worked. The key in our case was that the rays had to sync believably with the images, and the images were likely to change at the last minute, so I couldn’t go rebuilding the whole thing every time we got a revision.
Anyhoo, the end result is below. Let me know if that helps at all, I don’t have access to the setup, but I’d be happy to boot up flame and see if I can rebuild it if you’d like something clarified.