Ajax.PeriodicalUpdater — only update if the content has changed?

I’m using the following code in conjunction with the Prototype library:

new Ajax.PeriodicalUpdater(‘activity’, ‘activity.output.php’, { method: ‘get’, frequency: 1, decay: 2, insertion: Insertion.Top });

and was wondering if there’s any way to prevent the PeriodicalUpdater from processing the update if the output hasn’t changed? It already decays nicely, but how can I prevent it from updating if there’s no change?

http://www.prototypejs.org/api/ajax/periodicalUpdater