Leave the connection open, until an event occurs.
Have a look at Django / Comet (Push): Least of all evils? or The latest recommendation for Comet in Python? - COMET is another name for "ajax long-polling".
Apparently the most common approach is not doing it directly in django but with the help of an additional daemon (probably because e.g. Apache doesn't do well with lots of long-living connections). Nowadays nodejs+socketio is pretty popular for this (and it can even use WebSockets) - you just need to find a nice way to pass data between the two things. If it's unidirectional (e.g. just broadcasts to all connected clients) a redis pubsub queue is not a bad option for this.
But http://code.google.com/p/django-orbited/ is probably the most djangoish solution.
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