This definitely sounds like a rather perfect compositing situation to me, and BI might be a simple way to get that “window glow” part of it.
Treat the two objectives separately. The “money shot” part of it is being able to look inside all of those windows and to see offices. Use Cycles for that, but while doing so, forget about the glow. Next, use “whatever means” to get (at least, the location of …) “the glow,” without worrying about offices.
Now, you have two channels of information. “Mix them down.” Take the glow-channel, maybe fiddle with its color, blur the heck out of it, maybe streak it in a particular direction, desaturate it, and then add the two channels together.
My point is: once you’ve got those two two-dee channels of information set into your “digital mixing board,” you can tweak the shot in real time until it’s perfect. (“All your rendering days are done.”)
None other than Ansel Adams once said that, “a photograph is captured in the camera, but it’s made in the darkroom.” And it’s 100% true. You don’t have to make the entire effect come together, “like Venus :eek: popping out :eek: from a clamshell on the beach.” Split the shot into n pieces, get each one of them “pristine and isolated,” then “mix them down” to taste.