maybe you could work with ajax in a webbrowser. The engine produces for every user on the webpage an image and then an ajax script could request an image and send back the controls of the user(keystates). But that ofc would be really slow, maybe after 3 seconds a new image, if the connection is good.

But couldn't you try to make a lot of 360° shots of the level and the user can choose of them? maybe that would be a better way...also for users with a slow connection