While not strictly within your requirements, you could one of the many HTML/Javascript based plotting libraries and feed it pseudo-realtime data via websockets. This demo does it, except without the websockets part.

Or you could code your own webbased solution with HTML5 Canvas and websockets, for which it is also very easy to feed back user interactrion to your backend. While not a graph, a demo of the technology is here on my blog, and a description about interprocess messaging with Net::Clacks to feed data between the webserver and the backend is here: Interprocess messaging with Net::Clacks

Of course, this is only the way i would have solve, or rather have solved it in the past. And yes, this post is a shameless plug for my very own Net::Clacks ;-)