I think there is a good solution to your problem. Several of my scripts use invisible follower tokens (Torch's flickers, Bump, Facing). Probably I'd suggest making a script that lets you toggle on a follower for players which has sight, is controlled by all players, pushed to the back below tokens, and undoes any changes made to it so that it always just stays where it's suppose to be granting sight to the other players. I don't have time to write it right now (prepping for my sunday game, working on a rewrite), but I can help you with it or work on it later. I'd suggest using Facing as a base, but have it create the image that Bump and Torch use (clear 1x1 gif). Then it's just a matter of juggling the layers and players on it.